99 Commits
Author SHA1 Message Date
Kees CookandLinus Torvalds 189f164e57 Convert remaining multi-line kmalloc_obj/flex GFP_KERNEL uses
Conversion performed via this Coccinelle script:

  // SPDX-License-Identifier: GPL-2.0-only
  // Options: --include-headers-for-types --all-includes --include-headers --keep-comments
  virtual patch

  @gfp depends on patch && !(file in "tools") && !(file in "samples")@
  identifier ALLOC = {kmalloc_obj,kmalloc_objs,kmalloc_flex,
 		    kzalloc_obj,kzalloc_objs,kzalloc_flex,
		    kvmalloc_obj,kvmalloc_objs,kvmalloc_flex,
		    kvzalloc_obj,kvzalloc_objs,kvzalloc_flex};
  @@

  	ALLOC(...
  -		, GFP_KERNEL
  	)

  $ make coccicheck MODE=patch COCCI=gfp.cocci

Build and boot tested x86_64 with Fedora 42's GCC and Clang:

Linux version 6.19.0+ (user@host) (gcc (GCC) 15.2.1 20260123 (Red Hat 15.2.1-7), GNU ld version 2.44-12.fc42) #1 SMP PREEMPT_DYNAMIC 1970-01-01
Linux version 6.19.0+ (user@host) (clang version 20.1.8 (Fedora 20.1.8-4.fc42), LLD 20.1.8) #1 SMP PREEMPT_DYNAMIC 1970-01-01

Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2026-02-22 08:26:33 -08:00
Kees Cook 69050f8d6d treewide: Replace kmalloc with kmalloc_obj for non-scalar types
This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:

Single allocations:	kmalloc(sizeof(TYPE), ...)
are replaced with:	kmalloc_obj(TYPE, ...)

Array allocations:	kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with:	kmalloc_objs(TYPE, COUNT, ...)

Flex array allocations:	kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with:	kmalloc_flex(*PTR, FAM, COUNT, ...)

(where TYPE may also be *VAR)

The resulting allocations no longer return "void *", instead returning
"TYPE *".

Signed-off-by: Kees Cook <kees@kernel.org>
2026-02-21 01:02:28 -08:00
Roman KiselandWei Liu b537794bc2 Drivers: hv: Set the default VMBus version to 6.0
The confidential VMBus is supported by the protocol version
6.0 onwards.

Attempt to establish the VMBus 6.0 connection thus enabling
the confidential VMBus features when available.

Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2025-11-15 06:18:15 +00:00
Roman KiselandWei Liu bf35d298bb Drivers: hv: Support confidential VMBus channels
To make use of Confidential VMBus channels, initialize the
co_ring_buffers and co_external_memory fields of the channel
structure.

Advertise support upon negotiating the version and compute
values for those fields and initialize them.

Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2025-11-15 06:18:15 +00:00
Nuno Das NevesandWei Liu 36c46e64c5 Drivers: hv: Use nested hypercall for post message and signal event
When running nested, these hypercalls must be sent to the L0 hypervisor
or VMBus will fail.

Remove hv_do_nested_hypercall() and hv_do_fast_nested_hypercall8()
altogether and open-code these cases, since there are only 2 and all
they do is add the nested bit.

Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Roman Kisel <romank@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/1752261532-7225-2-git-send-email-nunodasneves@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <1752261532-7225-2-git-send-email-nunodasneves@linux.microsoft.com>
2025-07-15 06:24:16 +00:00
Long LiandWei Liu 09eea7ad0b Drivers: hv: Allocate interrupt and monitor pages aligned to system page boundary
There are use cases that interrupt and monitor pages are mapped to
user-mode through UIO, so they need to be system page aligned. Some
Hyper-V allocation APIs introduced earlier broke those requirements.

Fix this by using page allocation functions directly for interrupt
and monitor pages.

Cc: stable@vger.kernel.org
Fixes: ca48739e59 ("Drivers: hv: vmbus: Move Hyper-V page allocator to arch neutral code")
Signed-off-by: Long Li <longli@microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/1746492997-4599-2-git-send-email-longli@linuxonhyperv.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <1746492997-4599-2-git-send-email-longli@linuxonhyperv.com>
2025-05-23 16:30:56 +00:00
Naman JainandWei Liu 113386ca98 Drivers: hv: vmbus: Wait for boot-time offers during boot and resume
Channel offers are requested during VMBus initialization and resume from
hibernation. Add support to wait for all boot-time channel offers to
be delivered and processed before returning from vmbus_request_offers.

This is in analogy to a PCI bus not returning from probe until it has
scanned all devices on the bus.

Without this, user mode can race with VMBus initialization and miss
channel offers. User mode has no way to work around this other than
sleeping for a while, since there is no way to know when VMBus has
finished processing boot-time offers.

With this added functionality, remove earlier logic which keeps track
of count of offered channels post resume from hibernation. Once all
offers delivered message is received, no further boot-time offers are
going to be received. Consequently, logic to prevent suspend from
happening after previous resume had missing offers, is also removed.

Co-developed-by: John Starks <jostarks@microsoft.com>
Signed-off-by: John Starks <jostarks@microsoft.com>
Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>
Reviewed-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20250102130712.1661-2-namjain@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20250102130712.1661-2-namjain@linux.microsoft.com>
2025-01-10 00:54:21 +00:00
Rick EdgecombeandWei Liu 03f5a999ad Drivers: hv: vmbus: Leak pages if set_memory_encrypted() fails
In CoCo VMs it is possible for the untrusted host to cause
set_memory_encrypted() or set_memory_decrypted() to fail such that an
error is returned and the resulting memory is shared. Callers need to
take care to handle these errors to avoid returning decrypted (shared)
memory to the page allocator, which could lead to functional or security
issues.

VMBus code could free decrypted pages if set_memory_encrypted()/decrypted()
fails. Leak the pages if this happens.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lore.kernel.org/r/20240311161558.1310-2-mhklinux@outlook.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20240311161558.1310-2-mhklinux@outlook.com>
2024-04-10 21:33:32 +00:00
Linus Torvalds 0b90c5637d Merge tag 'hyperv-next-signed-20230902' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux
Pull hyperv updates from Wei Liu:

 - Support for SEV-SNP guests on Hyper-V (Tianyu Lan)

 - Support for TDX guests on Hyper-V (Dexuan Cui)

 - Use SBRM API in Hyper-V balloon driver (Mitchell Levy)

 - Avoid dereferencing ACPI root object handle in VMBus driver (Maciej
   Szmigiero)

 - A few misecllaneous fixes (Jiapeng Chong, Nathan Chancellor, Saurabh
   Sengar)

* tag 'hyperv-next-signed-20230902' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux: (24 commits)
  x86/hyperv: Remove duplicate include
  x86/hyperv: Move the code in ivm.c around to avoid unnecessary ifdef's
  x86/hyperv: Remove hv_isolation_type_en_snp
  x86/hyperv: Use TDX GHCI to access some MSRs in a TDX VM with the paravisor
  Drivers: hv: vmbus: Bring the post_msg_page back for TDX VMs with the paravisor
  x86/hyperv: Introduce a global variable hyperv_paravisor_present
  Drivers: hv: vmbus: Support >64 VPs for a fully enlightened TDX/SNP VM
  x86/hyperv: Fix serial console interrupts for fully enlightened TDX guests
  Drivers: hv: vmbus: Support fully enlightened TDX guests
  x86/hyperv: Support hypercalls for fully enlightened TDX guests
  x86/hyperv: Add hv_isolation_type_tdx() to detect TDX guests
  x86/hyperv: Fix undefined reference to isolation_type_en_snp without CONFIG_HYPERV
  x86/hyperv: Add missing 'inline' to hv_snp_boot_ap() stub
  hv: hyperv.h: Replace one-element array with flexible-array member
  Drivers: hv: vmbus: Don't dereference ACPI root object handle
  x86/hyperv: Add hyperv-specific handling for VMMCALL under SEV-ES
  x86/hyperv: Add smp support for SEV-SNP guest
  clocksource: hyper-v: Mark hyperv tsc page unencrypted in sev-snp enlightened guest
  x86/hyperv: Use vmmcall to implement Hyper-V hypercall in sev-snp enlightened guest
  drivers: hv: Mark percpu hvcall input arg page unencrypted in SEV-SNP enlightened guest
  ...
2023-09-04 11:26:29 -07:00
Dexuan CuiandWei Liu d3a9d7e49d x86/hyperv: Introduce a global variable hyperv_paravisor_present
The new variable hyperv_paravisor_present is set only when the VM
is a SNP/TDX VM with the paravisor running: see ms_hyperv_init_platform().

We introduce hyperv_paravisor_present because we can not use
ms_hyperv.paravisor_present in arch/x86/include/asm/mshyperv.h:

struct ms_hyperv_info is defined in include/asm-generic/mshyperv.h, which
is included at the end of arch/x86/include/asm/mshyperv.h, but at the
beginning of arch/x86/include/asm/mshyperv.h, we would already need to use
struct ms_hyperv_info in hv_do_hypercall().

We use hyperv_paravisor_present only in include/asm-generic/mshyperv.h,
and use ms_hyperv.paravisor_present elsewhere. In the future, we'll
introduce a hypercall function structure for different VM types, and
at boot time, the right function pointers would be written into the
structure so that runtime testing of TDX vs. SNP vs. normal will be
avoided and hyperv_paravisor_present will no longer be needed.

Call hv_vtom_init() when it's a VBS VM or when ms_hyperv.paravisor_present
is true, i.e. the VM is a SNP VM or TDX VM with the paravisor.

Enhance hv_vtom_init() for a TDX VM with the paravisor.

In hv_common_cpu_init(), don't decrypt the hyperv_pcpu_input_arg
for a TDX VM with the paravisor, just like we don't decrypt the page
for a SNP VM with the paravisor.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230824080712.30327-7-decui@microsoft.com
2023-08-25 00:04:57 +00:00
Tianyu LanandWei Liu 8387ce06d7 x86/hyperv: Set Virtual Trust Level in VMBus init message
SEV-SNP guests on Hyper-V can run at multiple Virtual Trust
Levels (VTL).  During boot, get the VTL at which we're running
using the GET_VP_REGISTERs hypercall, and save the value
for future use.  Then during VMBus initialization, set the VTL
with the saved value as required in the VMBus init message.

Reviewed-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <tiala@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230818102919.1318039-3-ltykernel@gmail.com
2023-08-22 00:38:20 +00:00
Kameron CarrandWei Liu a6fe043880 Drivers: hv: Change hv_free_hyperv_page() to take void * argument
Currently hv_free_hyperv_page() takes an unsigned long argument, which
is inconsistent with the void * return value from the corresponding
hv_alloc_hyperv_page() function and variants. This creates unnecessary
extra casting.

Change the hv_free_hyperv_page() argument type to void *.
Also remove redundant casts from invocations of
hv_alloc_hyperv_page() and variants.

Signed-off-by: Kameron Carr <kameroncarr@linux.microsoft.com>
Reviewed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Link: https://lore.kernel.org/r/1687558189-19734-1-git-send-email-kameroncarr@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2023-06-28 17:51:18 +00:00
Michael KelleyandWei Liu a5ddb74588 Drivers: hv: vmbus: Remove second mapping of VMBus monitor pages
With changes to how Hyper-V guest VMs flip memory between private
(encrypted) and shared (decrypted), creating a second kernel virtual
mapping for shared memory is no longer necessary.  Everything needed
for the transition to shared is handled by set_memory_decrypted().

As such, remove the code to create and manage the second
mapping for VMBus monitor pages. Because set_memory_decrypted()
and set_memory_encrypted() are no-ops in normal VMs, it's
not even necessary to test for being in a Confidential VM
(a.k.a., "Isolation VM").

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Link: https://lore.kernel.org/r/1679838727-87310-9-git-send-email-mikelley@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2023-04-17 19:19:04 +00:00
Mohammed GamalandWei Liu 1eb65c8687 Drivers: vmbus: Check for channel allocation before looking up relids
relid2channel() assumes vmbus channel array to be allocated when called.
However, in cases such as kdump/kexec, not all relids will be reset by the host.
When the second kernel boots and if the guest receives a vmbus interrupt during
vmbus driver initialization before vmbus_connect() is called, before it finishes,
or if it fails, the vmbus interrupt service routine is called which in turn calls
relid2channel() and can cause a null pointer dereference.

Print a warning and error out in relid2channel() for a channel id that's invalid
in the second kernel.

Fixes: 8b6a877c06 ("Drivers: hv: vmbus: Replace the per-CPU channel lists with a global array of channels")

Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Link: https://lore.kernel.org/r/20230217204411.212709-1-mgamal@redhat.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2023-03-06 15:28:03 +00:00
Saurabh SengarandWei Liu 78c65f0f3c Drivers: hv: vmbus: Optimize vmbus_on_event
In the vmbus_on_event loop, 2 jiffies timer will not serve the purpose if
callback_fn takes longer. For effective use move this check inside of
callback functions where needed. Out of all the VMbus drivers using
vmbus_on_event, only storvsc has a high packet volume, thus add this limit
only in storvsc callback for now.
There is no apparent benefit of loop itself because this tasklet will be
scheduled anyway again if there are packets left in ring buffer. This
patch removes this unnecessary loop as well.

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1658741848-4210-1-git-send-email-ssengar@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2022-09-23 09:27:17 +00:00
Shradha GuptaandWei Liu 52be93558a Drivers: hv: vm_bus: Handle vmbus rescind calls after vmbus is suspended
Add a flag to indicate that the vmbus is suspended so we should ignore
any offer message. Add a new work_queue for rescind msg, so we could drain
it along with other offer work_queues upon suspension.
It was observed that in some hibernation related scenario testing, after
vmbus_bus_suspend() we get rescind offer message for the vmbus. This would
lead to processing of a rescind message for a channel that has already been
suspended.

Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20220711041147.GA5569@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2022-07-11 18:53:42 +00:00
Michael KelleyandWei Liu a6b94c6b49 Drivers: hv: vmbus: Remove support for Hyper-V 2008 and Hyper-V 2008R2/Win7
The VMbus driver has special case code for running on the first released
versions of Hyper-V: 2008 and 2008 R2/Windows 7. These versions are now
out of support (except for extended security updates) and lack the
performance features needed for effective production usage of Linux
guests.

Simplify the code by removing the negotiation of the VMbus protocol
versions required for these releases of Hyper-V, and by removing the
special case code for handling these VMbus protocol versions.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/1651509391-2058-2-git-send-email-mikelley@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2022-05-11 17:49:49 +00:00
Tianyu LanandWei Liu f2f136c05f Drivers: hv: vmbus: Add SNP support for VMbus channel initiate message
The monitor pages in the CHANNELMSG_INITIATE_CONTACT msg are shared
with host in Isolation VM and so it's necessary to use hvcall to set
them visible to host. In Isolation VM with AMD SEV SNP, the access
address should be in the extra space which is above shared gpa
boundary. So remap these pages into the extra address(pa +
shared_gpa_boundary).

Introduce monitor_pages_original[] in the struct vmbus_connection
to store monitor page virtual address returned by hv_alloc_hyperv_
zeroed_page() and free monitor page via monitor_pages_original in
the vmbus_disconnect(). The monitor_pages[] is to used to access
monitor page and it is initialized to be equal with monitor_pages_
original. The monitor_pages[] will be overridden in the isolation VM
with va of extra address. Introduce monitor_pages_pa[] to store
monitor pages' physical address and use it to populate pa in the
initiate msg.

Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Link: https://lore.kernel.org/r/20211025122116.264793-9-ltykernel@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2021-10-28 11:22:55 +00:00
Tianyu LanandWei Liu 20c89a559e x86/hyperv: Add ghcb hvcall support for SNP VM
hyperv provides ghcb hvcall to handle VMBus
HVCALL_SIGNAL_EVENT and HVCALL_POST_MESSAGE
msg in SNP Isolation VM. Add such support.

Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Link: https://lore.kernel.org/r/20211025122116.264793-8-ltykernel@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2021-10-28 11:22:49 +00:00
Jiapeng ChongandWei Liu 9de6655cc5 drivers: hv: Fix missing error code in vmbus_connect()
Eliminate the follow smatch warning:

drivers/hv/connection.c:236 vmbus_connect() warn: missing error code
'ret'.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1621940321-72353-1-git-send-email-jiapeng.chong@linux.alibaba.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2021-06-02 15:16:36 +00:00
Andrea Parri (Microsoft)andWei Liu 8c2d5e0640 Drivers: hv: vmbus: Initialize unload_event statically
If a malicious or compromised Hyper-V sends a spurious message of type
CHANNELMSG_UNLOAD_RESPONSE, the function vmbus_unload_response() will
call complete() on an uninitialized event, and cause an oops.

Reported-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20210420014350.2002-1-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2021-04-20 19:40:17 +00:00
Andrea Parri (Microsoft)andWei Liu 1df53d212c Drivers: hv: vmbus: Introduce and negotiate VMBus protocol version 5.3
Hyper-V has added VMBus protocol version 5.3.  Allow Linux guests to
negotiate the new version on version of Hyper-V that support it.

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20210416143449.16185-2-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2021-04-18 13:03:11 +00:00
VasanthandWei Liu f850a4cad2 drivers: hv: Fix whitespace errors
Fixed checkpatch warning and errors on hv driver.

Signed-off-by: Vasanth Mathivanan <vasanth3g@gmail.com>
Link: https://lore.kernel.org/r/20210219171311.421961-1-vasanth3g@gmail.com
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2021-03-08 17:32:58 +00:00
Andrea Parri (Microsoft)andWei Liu 7ef4b2f0d9 Drivers: hv: vmbus: Enforce 'VMBus version >= 5.2' on isolated guests
Restrict the protocol version(s) that will be negotiated with the host
to be 5.2 or greater if the guest is running isolated.  This reduces the
footprint of the code that will be exercised by Confidential VMs and
hence the exposure to bugs and vulnerabilities.

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20210201144814.2701-4-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2021-02-11 08:47:05 +00:00
Andrea Parri (Microsoft)andWei Liu 8b6a877c06 Drivers: hv: vmbus: Replace the per-CPU channel lists with a global array of channels
When Hyper-V sends an interrupt to the guest, the guest has to figure
out which channel the interrupt is associated with.  Hyper-V sets a bit
in a memory page that is shared with the guest, indicating a particular
"relid" that the interrupt is associated with.  The current Linux code
then uses a set of per-CPU linked lists to map a given "relid" to a
pointer to a channel structure.

This design introduces a synchronization problem if the CPU that Hyper-V
will interrupt for a certain channel is changed.  If the interrupt comes
on the "old CPU" and the channel was already moved to the per-CPU list
of the "new CPU", then the relid -> channel mapping will fail and the
interrupt is dropped.  Similarly, if the interrupt comes on the new CPU
but the channel was not moved to the per-CPU list of the new CPU, then
the mapping will fail and the interrupt is dropped.

Relids are integers ranging from 0 to 2047.  The mapping from relids to
channel structures can be done by setting up an array with 2048 entries,
each entry being a pointer to a channel structure (hence total size ~16K
bytes, which is not a problem).  The array is global, so there are no
per-CPU linked lists to update.  The array can be searched and updated
by loading from/storing to the array at the specified index.  With no
per-CPU data structures, the above mentioned synchronization problem is
avoided and the relid2channel() function gets simpler.

Suggested-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20200406001514.19876-4-parri.andrea@gmail.com
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
2020-04-23 13:17:11 +00:00