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SubjectRe: [PATCH 2/2] KVM: VMX: Add Force Emulation Prefix for "emulate the next instruction"
On Mon, Mar 26, 2018 at 07:12:15PM -0700, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
>
> This patch introduces a Force Emulation Prefix (ud2a; .ascii "kvm") for
> "emulate the next instruction", the codes will be executed by emulator
> instead of processor, for testing purposes.

Can you expand a bit ? Why do you want this in KVM in the first place?
Should this be controlled by a boolean parameter?
>
> A testcase here:
>
> #include <stdio.h>
> #include <string.h>
>
> #define HYPERVISOR_INFO 0x40000000
>
> #define CPUID(idx, eax, ebx, ecx, edx)\
> asm volatile (\
> "ud2a; .ascii \"kvm\"; 1: cpuid" \
> :"=b" (*ebx), "=a" (*eax),"=c" (*ecx), "=d" (*edx)\
> :"0"(idx) );
>
> void main()
> {
> unsigned int eax,ebx,ecx,edx;
> char string[13];
>
> CPUID(HYPERVISOR_INFO, &eax, &ebx, &ecx, &edx);
> *(unsigned int *)(string+0) = ebx;
> *(unsigned int *)(string+4) = ecx;
> *(unsigned int *)(string+8) = edx;
>
> string[12] = 0;
> if (strncmp(string, "KVMKVMKVM\0\0\0",12) == 0)
> printf("kvm guest\n");
> else
> printf("bare hardware\n");
> }
>
> Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> arch/x86/kvm/vmx.c | 18 +++++++++++++++++-
> 1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 0f99833..90abed8 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -108,6 +108,9 @@ module_param_named(enable_shadow_vmcs, enable_shadow_vmcs, bool, S_IRUGO);
> static bool __read_mostly nested = 0;
> module_param(nested, bool, S_IRUGO);
>
> +static bool __read_mostly fep = 0;
> +module_param(fep, bool, S_IRUGO);
> +
> static u64 __read_mostly host_xss;
>
> static bool __read_mostly enable_pml = 1;
> @@ -6218,8 +6221,21 @@ static int handle_machine_check(struct kvm_vcpu *vcpu)
> static int handle_ud(struct kvm_vcpu *vcpu)
> {
> enum emulation_result er;
> + int emulation_type = EMULTYPE_TRAP_UD;
> +
> + if (fep) {
> + char sig[5]; /* ud2; .ascii "kvm" */
> + struct x86_exception e;

Don't you want to do = { };
to memset it?
> +
> + kvm_read_guest_virt(&vcpu->arch.emulate_ctxt,
> + kvm_get_linear_rip(vcpu), sig, sizeof(sig), &e);
> + if (memcmp(sig, "\xf\xbkvm", sizeof(sig)) == 0) {
> + emulation_type = 0;
> + kvm_rip_write(vcpu, kvm_rip_read(vcpu) + sizeof(sig));
> + }
> + }
>
> - er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD);
> + er = emulate_instruction(vcpu, emulation_type);
> if (er == EMULATE_USER_EXIT)
> return 0;
> if (er != EMULATE_DONE)
> --
> 2.7.4
>

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