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kvm: set CR4.PGE

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```
CR4.PGE (bit-7) enables Paging Global Extensions (PGE). PGE determines whether
moves to CR3 flush all of the PTE's from the TLB, or only those whose G-bit
(global bit) is not set. Likewise, for task switches which implicitly set CR3,
CR4.PGE controls TLB flushing in the same manner.
```

In case of gvisor, it improves performance of switching to/from the Sentry:
          │     kvm     │               kvm.pge               │
          │ wall_ns/op  │ wall_ns/op   vs base                │
Getpid      1.774k ± 0%   1.607k ± 1%   -9.36% (p=0.000 n=10)
GetpidOpt   1.623k ± 1%   1.452k ± 1%  -10.54% (p=0.000 n=10)
geomean     1.696k        1.528k        -9.95%

          │     kvm     │               kvm.pge               │
          │  cpu_ns/op  │  cpu_ns/op   vs base                │
Getpid      1.749k ± 0%   1.583k ± 1%   -9.52% (p=0.000 n=10)
GetpidOpt   1.600k ± 0%   1.414k ± 2%  -11.62% (p=0.000 n=10)
geomean     1.673k        1.496k       -10.58%

It plays only on hosts without PCID.

PiperOrigin-RevId: 671587163
This commit is contained in:
Andrei Vagin
2024-09-05 19:08:08 -07:00
committed by gVisor bot
parent 15d2cdc331
commit c0d0fb0677
1 changed files with 1 additions and 1 deletions
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pkg/ring0/kernel_amd64.go
+1 -1
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@@ -186,7 +186,7 @@ func (c *CPU) CR0() uint64 {
//
//go:nosplit
func (c *CPU) CR4() uint64 {
cr4 := uint64(_CR4_PAE | _CR4_PSE | _CR4_OSFXSR | _CR4_OSXMMEXCPT)
cr4 := uint64(_CR4_PAE | _CR4_PSE | _CR4_PGE | _CR4_OSFXSR | _CR4_OSXMMEXCPT)
if hasPCID {
cr4 |= _CR4_PCIDE
}