Providing a helper function to update HOST_RSP is visibly easier to
read, and more importantly (for the future) eliminates two arguments to
the VM-Enter assembly blob. Reducing the number of arguments to the asm
blob is for all intents and purposes a prerequisite to moving the code
to a proper assembly routine. It's not truly mandatory, but it greatly
simplifies the future code, and the cost of the extra CALL+RET is
negligible in the grand scheme.
Tweak the comment about clearing "clobbered" registers. The trigger
isn't actually whether a register is marked as clobbered, but whether
it will hold a guest value at the end of the asm blob. This matters now
that RCX is clobbered but holds a host-defined value.
Note that although _ASM_ARG[1-3] can be used in the inline asm itself,
the intput/output constraints need to be manually defined. gcc will
actually compile with _ASM_ARG[1-3] specified as constraints, but what
it actually ends up doing with the bogus constraint is unknown.
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/kvm/vmx/vmx.c | 55 +++++++++++++++++++++---------------------
1 file changed, 28 insertions(+), 27 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 57c51c51adbf..ba22b59bb874 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6362,15 +6362,18 @@ static void vmx_update_hv_timer(struct kvm_vcpu *vcpu)
vmx->loaded_vmcs->hv_timer_armed = false;
}
+void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp)
+{
+ if (unlikely(host_rsp != vmx->loaded_vmcs->host_state.rsp)) {
+ vmx->loaded_vmcs->host_state.rsp = host_rsp;
+ vmcs_writel(HOST_RSP, host_rsp);
+ }
+}
+
static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
{
- unsigned long evmcs_rsp;
-
vmx->__launched = vmx->loaded_vmcs->launched;
- evmcs_rsp = static_branch_unlikely(&enable_evmcs) ?
- (unsigned long)¤t_evmcs->host_rsp : 0;
-
if (static_branch_unlikely(&vmx_l1d_should_flush))
vmx_l1d_flush(vcpu);
@@ -6381,21 +6384,14 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
/* Store host registers */
"push %%" _ASM_BP " \n\t"
"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* placeholder for guest RCX */
- "push %%" _ASM_CX " \n\t"
- "sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */
- "cmp %%" _ASM_SP ", (%%" _ASM_DI ") \n\t"
- "je 1f \n\t"
- "mov %%" _ASM_SP ", (%%" _ASM_DI ") \n\t"
- /* Avoid VMWRITE when Enlightened VMCS is in use */
- "test %%" _ASM_SI ", %%" _ASM_SI " \n\t"
- "jz 2f \n\t"
- "mov %%" _ASM_SP ", (%%" _ASM_SI ") \n\t"
- "jmp 1f \n\t"
- "2: \n\t"
- "mov $%c[HOST_RSP], %%" _ASM_DX " \n\t"
- __ex("vmwrite %%" _ASM_SP ", %%" _ASM_DX) "\n\t"
- "1: \n\t"
- "add $%c[wordsize], %%" _ASM_SP "\n\t" /* un-adjust RSP */
+ "push %%" _ASM_ARG1 " \n\t"
+
+ /* Adjust RSP to account for the CALL to vmx_vmenter(). */
+ "lea -%c[wordsize](%%" _ASM_SP "), %%" _ASM_ARG2 " \n\t"
+ "call vmx_update_host_rsp \n\t"
+
+ /* Load the vcpu_vmx pointer to RCX. */
+ "mov (%%" _ASM_SP "), %%" _ASM_CX " \n\t"
/* Check if vmlaunch or vmresume is needed */
"cmpb $0, %c[launched](%%" _ASM_CX ") \n\t"
@@ -6449,8 +6445,8 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
"mov %%r14, %c[r14](%%" _ASM_CX ") \n\t"
"mov %%r15, %c[r15](%%" _ASM_CX ") \n\t"
/*
- * Clear host registers marked as clobbered to prevent
- * speculative use.
+ * Clear registers that contain guest values and will not be
+ * restored to prevent speculative use of the guest's values.
*/
"xor %%r8d, %%r8d \n\t"
"xor %%r9d, %%r9d \n\t"
@@ -6467,11 +6463,16 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
"xor %%esi, %%esi \n\t"
"xor %%edi, %%edi \n\t"
"pop %%" _ASM_BP " \n\t"
- : ASM_CALL_CONSTRAINT, "=D"((int){0}), "=S"((int){0})
- : "c"(vmx), "D"(&vmx->loaded_vmcs->host_state.rsp), "S"(evmcs_rsp),
+ : ASM_CALL_CONSTRAINT,
+#ifdef CONFIG_X86_64
+ "=D"((int){0})
+ : "D"(vmx),
+#else
+ "=a"((int){0})
+ : "a"(vmx),
+#endif
[launched]"i"(offsetof(struct vcpu_vmx, __launched)),
[fail]"i"(offsetof(struct vcpu_vmx, fail)),
- [HOST_RSP]"i"(HOST_RSP),
[rax]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RAX])),
[rbx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RBX])),
[rcx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RCX])),
@@ -6492,10 +6493,10 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
[wordsize]"i"(sizeof(ulong))
: "cc", "memory"
#ifdef CONFIG_X86_64
- , "rax", "rbx", "rdx"
+ , "rax", "rbx", "rcx", "rdx", "rsi"
, "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
#else
- , "eax", "ebx", "edx"
+ , "ebx", "ecx", "edx", "edi", "esi"
#endif
);
--
2.20.1
