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KVM: SVM: Save/restore args across SEV-ES VMRUN via host save area

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Use the host save area to preserve volatile registers that are used in
__svm_sev_es_vcpu_run() to access function parameters after #VMEXIT.
Like saving/restoring non-volatile registers, there's no reason not to
take advantage of hardware restoring registers on #VMEXIT, as doing so
shaves a few instructions and the save area is going to be accessed no
matter what.

Converting all register save/restore code to use the host save area also
make it easier to follow the SEV-ES VMRUN flow in its entirety, as
opposed to having a mix of stack-based versus host save area save/restore.

Add a parameter to RESTORE_HOST_SPEC_CTRL_BODY so that the SEV-ES path
doesn't need to write @spec_ctrl_intercepted to memory just to play nice
with the common macro.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240223204233.3337324-7-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2024-02-23 12:42:31 -08:00
parent c92be2fd8e
commit adac42bf42
1 changed files with 13 additions and 16 deletions
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29
arch/x86/kvm/svm/vmenter.S
View File

@@ -67,7 +67,7 @@
"", X86_FEATURE_V_SPEC_CTRL
901:
.endm
.macro RESTORE_HOST_SPEC_CTRL_BODY
.macro RESTORE_HOST_SPEC_CTRL_BODY spec_ctrl_intercepted:req
900:
/* Same for after vmexit. */
mov $MSR_IA32_SPEC_CTRL, %ecx
@@ -76,7 +76,7 @@
* Load the value that the guest had written into MSR_IA32_SPEC_CTRL,
* if it was not intercepted during guest execution.
*/
cmpb $0, (%_ASM_SP)
cmpb $0, \spec_ctrl_intercepted
jnz 998f
rdmsr
movl %eax, SVM_spec_ctrl(%_ASM_DI)
@@ -269,7 +269,7 @@ SYM_FUNC_START(__svm_vcpu_run)
RET
RESTORE_GUEST_SPEC_CTRL_BODY
RESTORE_HOST_SPEC_CTRL_BODY
RESTORE_HOST_SPEC_CTRL_BODY (%_ASM_SP)
10: cmpb $0, _ASM_RIP(kvm_rebooting)
jne 2b
@@ -298,6 +298,8 @@ SYM_FUNC_END(__svm_vcpu_run)
#define SEV_ES_GPRS_BASE 0x300
#define SEV_ES_RBX (SEV_ES_GPRS_BASE + __VCPU_REGS_RBX * WORD_SIZE)
#define SEV_ES_RBP (SEV_ES_GPRS_BASE + __VCPU_REGS_RBP * WORD_SIZE)
#define SEV_ES_RSI (SEV_ES_GPRS_BASE + __VCPU_REGS_RSI * WORD_SIZE)
#define SEV_ES_RDI (SEV_ES_GPRS_BASE + __VCPU_REGS_RDI * WORD_SIZE)
#define SEV_ES_R12 (SEV_ES_GPRS_BASE + __VCPU_REGS_R12 * WORD_SIZE)
#define SEV_ES_R13 (SEV_ES_GPRS_BASE + __VCPU_REGS_R13 * WORD_SIZE)
#define SEV_ES_R14 (SEV_ES_GPRS_BASE + __VCPU_REGS_R14 * WORD_SIZE)
@@ -322,11 +324,12 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
mov %r12, SEV_ES_R12 (%rdx)
mov %rbx, SEV_ES_RBX (%rdx)
/* Accessed directly from the stack in RESTORE_HOST_SPEC_CTRL. */
push %rsi
/* Save @svm. */
push %rdi
/*
* Save volatile registers that hold arguments that are needed after
* #VMEXIT (RDI=@svm and RSI=@spec_ctrl_intercepted).
*/
mov %rdi, SEV_ES_RDI (%rdx)
mov %rsi, SEV_ES_RSI (%rdx)
/* Clobbers RAX, RCX, RDX (@hostsa). */
RESTORE_GUEST_SPEC_CTRL
@@ -342,15 +345,12 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
2: cli
/* Pop @svm to RDI, guest registers have been saved already. */
pop %rdi
#ifdef CONFIG_MITIGATION_RETPOLINE
/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
#endif
/* Clobbers RAX, RCX, RDX, consumes RDI (@svm). */
/* Clobbers RAX, RCX, RDX, consumes RDI (@svm) and RSI (@spec_ctrl_intercepted). */
RESTORE_HOST_SPEC_CTRL
/*
@@ -362,13 +362,10 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
*/
UNTRAIN_RET_VM
/* "Pop" and discard @spec_ctrl_intercepted. */
pop %rax
RET
RESTORE_GUEST_SPEC_CTRL_BODY
RESTORE_HOST_SPEC_CTRL_BODY
RESTORE_HOST_SPEC_CTRL_BODY %sil
3: cmpb $0, kvm_rebooting(%rip)
jne 2b