supporting lazy-fpsimd in guest on Arm64

Several jobs were finished in this patch:
1, provide functions to get/set fpcr/fpsr/vregs
2, support lazy-fpsimd-context-switch in el1

Signed-off-by: Bin Lu <bin.lu@arm.com>

pkg/sentry/platform/ring0/BUILD

@@ -71,6 +71,7 @@ go_library(
         "lib_amd64.go",
         "lib_amd64.s",
         "lib_arm64.go",
+        "lib_arm64.s",
         "ring0.go",
     ],
     importpath = "gvisor.dev/gvisor/pkg/sentry/platform/ring0",

pkg/sentry/platform/ring0/defs_arm64.go

@@ -73,6 +73,9 @@ type CPUArchState struct {
 
 	// application context pointer.
 	appAddr uintptr
+
+	// lazyVFP is the value of cpacr_el1.
+	lazyVFP uintptr
 }
 
 // ErrorCode returns the last error code.

pkg/sentry/platform/ring0/entry_arm64.s

@@ -31,6 +31,11 @@
 #define RSV_REG 	R18_PLATFORM
 #define RSV_REG_APP 	R9
 
+#define FPEN_NOTRAP 	0x3
+#define FPEN_SHIFT 	20
+
+#define FPEN_ENABLE (FPEN_NOTRAP << FPEN_SHIFT)
+
 #define REGISTERS_SAVE(reg, offset) \
   MOVD R0, offset+PTRACE_R0(reg); \
   MOVD R1, offset+PTRACE_R1(reg); \
@@ -279,6 +284,16 @@
 #define IRQ_DISABLE \
 	MSR $2, DAIFClr;
 
+#define VFP_ENABLE \
+	MOVD $FPEN_ENABLE, R0; \
+	WORD $0xd5181040; \ //MSR R0, CPACR_EL1
+	ISB $15;
+
+#define VFP_DISABLE \
+	MOVD $0x0, R0; \
+	WORD $0xd5181040; \ //MSR R0, CPACR_EL1
+	ISB $15;
+
 #define KERNEL_ENTRY_FROM_EL0 \
 	SUB $16, RSP, RSP; \		// step1, save r18, r9 into kernel temporary stack.
 	STP (RSV_REG, RSV_REG_APP), 16*0(RSP); \
@@ -318,6 +333,11 @@ TEXT ·Halt(SB),NOSPLIT,$0
 	BNE mmio_exit
 	MOVD $0, CPU_REGISTERS+PTRACE_R9(RSV_REG)
 mmio_exit:
+	// Disable fpsimd.
+	WORD $0xd5381041 // MRS CPACR_EL1, R1
+	MOVD R1, CPU_LAZY_VFP(RSV_REG)
+	VFP_DISABLE
+
 	// MMIO_EXIT.
 	MOVD $0, R9
 	MOVD R0, 0xffff000000001000(R9)
@@ -382,6 +402,8 @@ TEXT ·El1_sync(SB),NOSPLIT,$0
 	BEQ el1_svc
 	CMP $ESR_ELx_EC_BREAKPT_CUR, R24
 	BGE el1_dbg
+	CMP $ESR_ELx_EC_FP_ASIMD, R24
+	BEQ el1_fpsimd_acc
 	B el1_invalid
 
 el1_da:
@@ -402,6 +424,10 @@ el1_svc:
 el1_dbg:
 	B ·Shutdown(SB)
 
+el1_fpsimd_acc:
+	VFP_ENABLE
+	B ·kernelExitToEl1(SB)  // Resume.
+
 el1_invalid:
 	B ·Shutdown(SB)
 

pkg/sentry/platform/ring0/lib_arm64.go

@@ -16,10 +16,24 @@
 
 package ring0
 
-// LoadFloatingPoint loads floating point state by the most efficient mechanism
-// available (set by Init).
-var LoadFloatingPoint func(*byte)
+// CPACREL1 returns the value of the CPACR_EL1 register.
+func CPACREL1() (value uintptr)
 
-// SaveFloatingPoint saves floating point state by the most efficient mechanism
-// available (set by Init).
-var SaveFloatingPoint func(*byte)
+// GetFPCR returns the value of FPCR register.
+func GetFPCR() (value uintptr)
+
+// SetFPCR writes the FPCR value.
+func SetFPCR(value uintptr)
+
+// GetFPSR returns the value of FPSR register.
+func GetFPSR() (value uintptr)
+
+// SetFPSR writes the FPSR value.
+func SetFPSR(value uintptr)
+
+// SaveVRegs saves V0-V31 registers.
+// V0-V31: 32 128-bit registers for floating point and simd.
+func SaveVRegs(*byte)
+
+// LoadVRegs loads V0-V31 registers.
+func LoadVRegs(*byte)

pkg/sentry/platform/ring0/lib_arm64.s

@@ -0,0 +1,118 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+TEXT ·CPACREL1(SB),NOSPLIT,$0-8
+	WORD $0xd5381041 	// MRS CPACR_EL1, R1
+	MOVD R1, ret+0(FP)
+	RET
+
+TEXT ·GetFPCR(SB),NOSPLIT,$0-8
+	WORD $0xd53b4201    	// MRS NZCV, R1
+	MOVD R1, ret+0(FP)
+	RET
+
+TEXT ·GetFPSR(SB),NOSPLIT,$0-8
+	WORD $0xd53b4421   	// MRS FPSR, R1
+	MOVD R1, ret+0(FP)
+	RET
+
+TEXT ·SetFPCR(SB),NOSPLIT,$0-8
+	MOVD addr+0(FP), R1
+	WORD $0xd51b4201  	// MSR R1, NZCV
+	RET
+
+TEXT ·SetFPSR(SB),NOSPLIT,$0-8
+	MOVD addr+0(FP), R1
+	WORD $0xd51b4421   	// MSR R1, FPSR
+	RET
+
+TEXT ·SaveVRegs(SB),NOSPLIT,$0-8
+	MOVD addr+0(FP), R0
+
+	// Skip aarch64_ctx, fpsr, fpcr.
+	FMOVD F0, 16*1(R0)
+	FMOVD F1, 16*2(R0)
+	FMOVD F2, 16*3(R0)
+	FMOVD F3, 16*4(R0)
+	FMOVD F4, 16*5(R0)
+	FMOVD F5, 16*6(R0)
+	FMOVD F6, 16*7(R0)
+	FMOVD F7, 16*8(R0)
+	FMOVD F8, 16*9(R0)
+	FMOVD F9, 16*10(R0)
+	FMOVD F10, 16*11(R0)
+	FMOVD F11, 16*12(R0)
+	FMOVD F12, 16*13(R0)
+	FMOVD F13, 16*14(R0)
+	FMOVD F14, 16*15(R0)
+	FMOVD F15, 16*16(R0)
+	FMOVD F16, 16*17(R0)
+	FMOVD F17, 16*18(R0)
+	FMOVD F18, 16*19(R0)
+	FMOVD F19, 16*20(R0)
+	FMOVD F20, 16*21(R0)
+	FMOVD F21, 16*22(R0)
+	FMOVD F22, 16*23(R0)
+	FMOVD F23, 16*24(R0)
+	FMOVD F24, 16*25(R0)
+	FMOVD F25, 16*26(R0)
+	FMOVD F26, 16*27(R0)
+	FMOVD F27, 16*28(R0)
+	FMOVD F28, 16*29(R0)
+	FMOVD F29, 16*30(R0)
+	FMOVD F30, 16*31(R0)
+	FMOVD F31, 16*32(R0)
+	ISB $15
+
+	RET
+
+TEXT ·LoadVRegs(SB),NOSPLIT,$0-8
+	MOVD addr+0(FP), R0
+
+	// Skip aarch64_ctx, fpsr, fpcr.
+	FMOVD 16*1(R0), F0
+	FMOVD 16*2(R0), F1
+	FMOVD 16*3(R0), F2
+	FMOVD 16*4(R0), F3
+	FMOVD 16*5(R0), F4
+	FMOVD 16*6(R0), F5
+	FMOVD 16*7(R0), F6
+	FMOVD 16*8(R0), F7
+	FMOVD 16*9(R0), F8
+	FMOVD 16*10(R0), F9
+	FMOVD 16*11(R0), F10
+	FMOVD 16*12(R0), F11
+	FMOVD 16*13(R0), F12
+	FMOVD 16*14(R0), F13
+	FMOVD 16*15(R0), F14
+	FMOVD 16*16(R0), F15
+	FMOVD 16*17(R0), F16
+	FMOVD 16*18(R0), F17
+	FMOVD 16*19(R0), F18
+	FMOVD 16*20(R0), F19
+	FMOVD 16*21(R0), F20
+	FMOVD 16*22(R0), F21
+	FMOVD 16*23(R0), F22
+	FMOVD 16*24(R0), F23
+	FMOVD 16*25(R0), F24
+	FMOVD 16*26(R0), F25
+	FMOVD 16*27(R0), F26
+	FMOVD 16*28(R0), F27
+	FMOVD 16*29(R0), F28
+	FMOVD 16*30(R0), F29
+	FMOVD 16*31(R0), F30
+	FMOVD 16*32(R0), F31
+	ISB $15
+
+	RET

pkg/sentry/platform/ring0/offsets_arm64.go

@@ -39,6 +39,7 @@ func Emit(w io.Writer) {
 	fmt.Fprintf(w, "#define CPU_TTBR0_APP        0x%02x\n", reflect.ValueOf(&c.ttbr0App).Pointer()-reflect.ValueOf(c).Pointer())
 	fmt.Fprintf(w, "#define CPU_VECTOR_CODE      0x%02x\n", reflect.ValueOf(&c.vecCode).Pointer()-reflect.ValueOf(c).Pointer())
 	fmt.Fprintf(w, "#define CPU_APP_ADDR         0x%02x\n", reflect.ValueOf(&c.appAddr).Pointer()-reflect.ValueOf(c).Pointer())
+	fmt.Fprintf(w, "#define CPU_LAZY_VFP         0x%02x\n", reflect.ValueOf(&c.lazyVFP).Pointer()-reflect.ValueOf(c).Pointer())
 
 	fmt.Fprintf(w, "\n// Bits.\n")
 	fmt.Fprintf(w, "#define _KERNEL_FLAGS        0x%02x\n", KernelFlagsSet)