KVM: VMX: Load/save guest CR2 via C code in __vmx_vcpu_run()

...to eliminate its parameter and struct vcpu_vmx offset definition
from the assembly blob.  Accessing CR2 from C versus assembly doesn't
change the likelihood of taking a page fault (and modifying CR2) while
it's loaded with the guest's value, so long as we don't do anything
silly between accessing CR2 and VM-Enter/VM-Exit.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 12bb61e..5e43999 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6375,6 +6375,9 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
        if (static_branch_unlikely(&vmx_l1d_should_flush))
                vmx_l1d_flush(vcpu);
 
+       if (vcpu->arch.cr2 != read_cr2())
+               write_cr2(vcpu->arch.cr2);
+
        asm(
                /* Store host registers */
                "push %%" _ASM_BP " \n\t"
@@ -6395,13 +6398,6 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
                "1: \n\t"
                "add $%c[wordsize], %%" _ASM_SP "\n\t" /* un-adjust RSP */
 
-               /* Reload cr2 if changed */
-               "mov %c[cr2](%%" _ASM_CX "), %%" _ASM_AX " \n\t"
-               "mov %%cr2, %%" _ASM_DX " \n\t"
-               "cmp %%" _ASM_AX ", %%" _ASM_DX " \n\t"
-               "je 3f \n\t"
-               "mov %%" _ASM_AX", %%cr2 \n\t"
-               "3: \n\t"
                /* Check if vmlaunch or vmresume is needed */
                "cmpb $0, %c[launched](%%" _ASM_CX ") \n\t"
                /* Load guest registers.  Don't clobber flags. */
@@ -6471,9 +6467,6 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
                "xor %%r14d, %%r14d \n\t"
                "xor %%r15d, %%r15d \n\t"
 #endif
-               "mov %%cr2, %%" _ASM_AX "   \n\t"
-               "mov %%" _ASM_AX ", %c[cr2](%%" _ASM_CX ") \n\t"
-
                "xor %%eax, %%eax \n\t"
                "xor %%ebx, %%ebx \n\t"
                "xor %%ecx, %%ecx \n\t"
@@ -6504,7 +6497,6 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
                [r14]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R14])),
                [r15]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R15])),
 #endif
-               [cr2]"i"(offsetof(struct vcpu_vmx, vcpu.arch.cr2)),
                [wordsize]"i"(sizeof(ulong))
              : "cc", "memory"
 #ifdef CONFIG_X86_64
@@ -6514,6 +6506,8 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
                , "eax", "ebx", "edx"
 #endif
              );
+
+       vcpu->arch.cr2 = read_cr2();
 }
 STACK_FRAME_NON_STANDARD(__vmx_vcpu_run);