[19/29] KVM: VMX: Don't save guest registers after VM-Fail
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Message ID 20190118212037.24412-20-sean.j.christopherson@intel.com
State New
Headers show
Series
  • KVM: VMX: Move vCPU-run to proper asm sub-routine
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Commit Message

Sean Christopherson Jan. 18, 2019, 9:20 p.m. UTC
A failed VM-Enter (obviously) didn't succeed, meaning the CPU never
executed an instrunction in guest mode and so can't have changed the
general purpose registers.

In addition to saving some instructions in the VM-Fail case, this also
provides a separate path entirely and thus an opportunity to propagate
the fail condition to vmx->fail via register without introducing undue
pain.  Using a register, as opposed to directly referencing vmx->fail,
eliminates the need to pass the offset of 'fail', which will simplify
moving the code to proper assembly in future patches.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/vmx/vmx.c | 34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)

Comments

Paolo Bonzini Jan. 22, 2019, 11:24 a.m. UTC | #1
On 18/01/19 22:20, Sean Christopherson wrote:
> +	      : ASM_CALL_CONSTRAINT, "=ebx"(vmx->fail),

This should be "=b".

Paolo

Patch
diff mbox series

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 2b01250794e8..687948fe6d42 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6415,6 +6415,7 @@  static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 
 		/* Enter guest mode */
 		"call vmx_vmenter\n\t"
+		"jbe 2f \n\t"
 
 		/* Temporarily save guest's RCX. */
 		"push %%" _ASM_CX " \n\t"
@@ -6422,9 +6423,6 @@  static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 		/* Reload the vcpu_vmx pointer to RCX. */
 		"mov %c[wordsize](%%" _ASM_SP "), %%" _ASM_CX " \n\t"
 
-		/* Set vmx->fail based on EFLAGS.{CF,ZF} */
-		"setbe %c[fail](%%" _ASM_CX ")\n\t"
-
 		/* Save all guest registers, including RCX from the stack */
 		"mov %%" _ASM_AX ", %c[rax](%%" _ASM_CX ") \n\t"
 		"mov %%" _ASM_BX ", %c[rbx](%%" _ASM_CX ") \n\t"
@@ -6442,10 +6440,17 @@  static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 		"mov %%r13, %c[r13](%%" _ASM_CX ") \n\t"
 		"mov %%r14, %c[r14](%%" _ASM_CX ") \n\t"
 		"mov %%r15, %c[r15](%%" _ASM_CX ") \n\t"
+#endif
+
+		/* Clear EBX to indicate VM-Exit (as opposed to VM-Fail). */
+		"xor %%ebx, %%ebx \n\t"
+
 		/*
-		* Clear registers that contain guest values and will not be
-		* restored to prevent speculative use of the guest's values.
-		*/
+		 * Clear registers that contain guest values and will not be
+		 * restored to prevent speculative use of the guest's values.
+		 */
+		"1: \n\t"
+#ifdef CONFIG_X86_64
 		"xor %%r8d,  %%r8d \n\t"
 		"xor %%r9d,  %%r9d \n\t"
 		"xor %%r10d, %%r10d \n\t"
@@ -6456,7 +6461,6 @@  static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 		"xor %%r15d, %%r15d \n\t"
 #endif
 		"xor %%eax, %%eax \n\t"
-		"xor %%ebx, %%ebx \n\t"
 		"xor %%edx, %%edx \n\t"
 		"xor %%esi, %%esi \n\t"
 		"xor %%edi, %%edi \n\t"
@@ -6464,7 +6468,20 @@  static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 		/* "POP" the vcpu_vmx pointer. */
 		"add $%c[wordsize], %%" _ASM_SP " \n\t"
 		"pop  %%" _ASM_BP " \n\t"
-	      : ASM_CALL_CONSTRAINT, "=b"((int){0}),
+		"jmp 3f \n\t"
+
+		/* VM-Fail.  Out-of-line to avoid a taken Jcc after VM-Exit. */
+		"2: \n\t"
+		"mov $1, %%ebx \n\t"
+		/*
+		 * RCX holds a guest value and it's not cleared in the common
+		 * exit path as VM-Exit reloads it with the vcpu_vmx pointer.
+		 */
+		"xor %%ecx, %%ecx \n\t"
+		"jmp 1b \n\t"
+		"3: \n\t"
+
+	      : ASM_CALL_CONSTRAINT, "=ebx"(vmx->fail),
 #ifdef CONFIG_X86_64
 		"=D"((int){0})
 	      : "D"(vmx),
@@ -6473,7 +6490,6 @@  static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 	      : "a"(vmx),
 #endif
 		"bl"(vmx->loaded_vmcs->launched),
-		[fail]"i"(offsetof(struct vcpu_vmx, fail)),
 		[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])),