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linux/arch/x86/kvm/svm/vmenter.S
Tom Lendacky 16809ecdc1 KVM: SVM: Provide an updated VMRUN invocation for SEV-ES guests 
The run sequence is different for an SEV-ES guest compared to a legacy or
even an SEV guest. The guest vCPU register state of an SEV-ES guest will
be restored on VMRUN and saved on VMEXIT. There is no need to restore the
guest registers directly and through VMLOAD before VMRUN and no need to
save the guest registers directly and through VMSAVE on VMEXIT.

Update the svm_vcpu_run() function to skip register state saving and
restoring and provide an alternative function for running an SEV-ES guest
in vmenter.S

Additionally, certain host state is restored across an SEV-ES VMRUN. As
a result certain register states are not required to be restored upon
VMEXIT (e.g. FS, GS, etc.), so only do that if the guest is not an SEV-ES
guest.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <fb1c66d32f2194e171b95fc1a8affd6d326e10c1.1607620209.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-12-15 05:20:59 -05:00

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/* SPDX-License-Identifier: GPL-2.0 */
#include <linux/linkage.h>
#include <asm/asm.h>
#include <asm/bitsperlong.h>
#include <asm/kvm_vcpu_regs.h>
#include <asm/nospec-branch.h>
#define WORD_SIZE (BITS_PER_LONG / 8)
/* Intentionally omit RAX as it's context switched by hardware */
#define VCPU_RCX __VCPU_REGS_RCX * WORD_SIZE
#define VCPU_RDX __VCPU_REGS_RDX * WORD_SIZE
#define VCPU_RBX __VCPU_REGS_RBX * WORD_SIZE
/* Intentionally omit RSP as it's context switched by hardware */
#define VCPU_RBP __VCPU_REGS_RBP * WORD_SIZE
#define VCPU_RSI __VCPU_REGS_RSI * WORD_SIZE
#define VCPU_RDI __VCPU_REGS_RDI * WORD_SIZE
#ifdef CONFIG_X86_64
#define VCPU_R8 __VCPU_REGS_R8 * WORD_SIZE
#define VCPU_R9 __VCPU_REGS_R9 * WORD_SIZE
#define VCPU_R10 __VCPU_REGS_R10 * WORD_SIZE
#define VCPU_R11 __VCPU_REGS_R11 * WORD_SIZE
#define VCPU_R12 __VCPU_REGS_R12 * WORD_SIZE
#define VCPU_R13 __VCPU_REGS_R13 * WORD_SIZE
#define VCPU_R14 __VCPU_REGS_R14 * WORD_SIZE
#define VCPU_R15 __VCPU_REGS_R15 * WORD_SIZE
#endif
.section .noinstr.text, "ax"
/**
* __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
* @vmcb_pa: unsigned long
* @regs: unsigned long * (to guest registers)
*/
SYM_FUNC_START(__svm_vcpu_run)
push %_ASM_BP
#ifdef CONFIG_X86_64
push %r15
push %r14
push %r13
push %r12
#else
push %edi
push %esi
#endif
push %_ASM_BX
/* Save @regs. */
push %_ASM_ARG2
/* Save @vmcb. */
push %_ASM_ARG1
/* Move @regs to RAX. */
mov %_ASM_ARG2, %_ASM_AX
/* Load guest registers. */
mov VCPU_RCX(%_ASM_AX), %_ASM_CX
mov VCPU_RDX(%_ASM_AX), %_ASM_DX
mov VCPU_RBX(%_ASM_AX), %_ASM_BX
mov VCPU_RBP(%_ASM_AX), %_ASM_BP
mov VCPU_RSI(%_ASM_AX), %_ASM_SI
mov VCPU_RDI(%_ASM_AX), %_ASM_DI
#ifdef CONFIG_X86_64
mov VCPU_R8 (%_ASM_AX), %r8
mov VCPU_R9 (%_ASM_AX), %r9
mov VCPU_R10(%_ASM_AX), %r10
mov VCPU_R11(%_ASM_AX), %r11
mov VCPU_R12(%_ASM_AX), %r12
mov VCPU_R13(%_ASM_AX), %r13
mov VCPU_R14(%_ASM_AX), %r14
mov VCPU_R15(%_ASM_AX), %r15
#endif
/* "POP" @vmcb to RAX. */
pop %_ASM_AX
/* Enter guest mode */
sti
1: vmload %_ASM_AX
jmp 3f
2: cmpb $0, kvm_rebooting
jne 3f
ud2
_ASM_EXTABLE(1b, 2b)
3: vmrun %_ASM_AX
jmp 5f
4: cmpb $0, kvm_rebooting
jne 5f
ud2
_ASM_EXTABLE(3b, 4b)
5: vmsave %_ASM_AX
jmp 7f
6: cmpb $0, kvm_rebooting
jne 7f
ud2
_ASM_EXTABLE(5b, 6b)
7:
cli
#ifdef CONFIG_RETPOLINE
/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
#endif
/* "POP" @regs to RAX. */
pop %_ASM_AX
/* Save all guest registers. */
mov %_ASM_CX, VCPU_RCX(%_ASM_AX)
mov %_ASM_DX, VCPU_RDX(%_ASM_AX)
mov %_ASM_BX, VCPU_RBX(%_ASM_AX)
mov %_ASM_BP, VCPU_RBP(%_ASM_AX)
mov %_ASM_SI, VCPU_RSI(%_ASM_AX)
mov %_ASM_DI, VCPU_RDI(%_ASM_AX)
#ifdef CONFIG_X86_64
mov %r8, VCPU_R8 (%_ASM_AX)
mov %r9, VCPU_R9 (%_ASM_AX)
mov %r10, VCPU_R10(%_ASM_AX)
mov %r11, VCPU_R11(%_ASM_AX)
mov %r12, VCPU_R12(%_ASM_AX)
mov %r13, VCPU_R13(%_ASM_AX)
mov %r14, VCPU_R14(%_ASM_AX)
mov %r15, VCPU_R15(%_ASM_AX)
#endif
/*
* Clear all general purpose registers except RSP and RAX to prevent
* speculative use of the guest's values, even those that are reloaded
* via the stack. In theory, an L1 cache miss when restoring registers
* could lead to speculative execution with the guest's values.
* Zeroing XORs are dirt cheap, i.e. the extra paranoia is essentially
* free. RSP and RAX are exempt as they are restored by hardware
* during VM-Exit.
*/
xor %ecx, %ecx
xor %edx, %edx
xor %ebx, %ebx
xor %ebp, %ebp
xor %esi, %esi
xor %edi, %edi
#ifdef CONFIG_X86_64
xor %r8d, %r8d
xor %r9d, %r9d
xor %r10d, %r10d
xor %r11d, %r11d
xor %r12d, %r12d
xor %r13d, %r13d
xor %r14d, %r14d
xor %r15d, %r15d
#endif
pop %_ASM_BX
#ifdef CONFIG_X86_64
pop %r12
pop %r13
pop %r14
pop %r15
#else
pop %esi
pop %edi
#endif
pop %_ASM_BP
ret
SYM_FUNC_END(__svm_vcpu_run)
/**
* __svm_sev_es_vcpu_run - Run a SEV-ES vCPU via a transition to SVM guest mode
* @vmcb_pa: unsigned long
*/
SYM_FUNC_START(__svm_sev_es_vcpu_run)
push %_ASM_BP
#ifdef CONFIG_X86_64
push %r15
push %r14
push %r13
push %r12
#else
push %edi
push %esi
#endif
push %_ASM_BX
/* Enter guest mode */
mov %_ASM_ARG1, %_ASM_AX
sti
1: vmrun %_ASM_AX
jmp 3f
2: cmpb $0, kvm_rebooting
jne 3f
ud2
_ASM_EXTABLE(1b, 2b)
3: cli
#ifdef CONFIG_RETPOLINE
/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
#endif
pop %_ASM_BX
#ifdef CONFIG_X86_64
pop %r12
pop %r13
pop %r14
pop %r15
#else
pop %esi
pop %edi
#endif
pop %_ASM_BP
ret
SYM_FUNC_END(__svm_sev_es_vcpu_run)
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