Re: [PATCH 3/3] KVM: x86: correct mwait and monitor emulation

Eric Northup
2014-06-18T17:59:17Z

On Wed, Jun 18, 2014 at 7:19 AM, Nadav Amit <namit@cs.technion.ac.il> wrote:
> mwait and monitor are currently handled as nop. Considering this behavior, they
> should still be handled correctly, i.e., check execution conditions and generate
> exceptions when required. mwait and monitor may also be executed in real-mode
> and are not handled in that case. This patch performs the emulation of
> monitor-mwait according to Intel SDM (other than checking whether interrupt can
> be used as a break event).
>
> Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
> ---
> arch/x86/kvm/emulate.c | 41 +++++++++++++++++++++++++++++++++++++++--
> arch/x86/kvm/svm.c | 22 ++--------------------
> arch/x86/kvm/vmx.c | 27 +++++++++++----------------
> 3 files changed, 52 insertions(+), 38 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index ef7a5a0..424b58d 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -3344,6 +3344,43 @@ static int em_bswap(struct x86_emulate_ctxt *ctxt)
> return X86EMUL_CONTINUE;
> }
>
> +static int em_monitor(struct x86_emulate_ctxt *ctxt)
> +{
> + int rc;
> + struct segmented_address addr;
> + u64 rcx = reg_read(ctxt, VCPU_REGS_RCX);
> + u64 rax = reg_read(ctxt, VCPU_REGS_RAX);
> + u8 byte;

I'd request:

u32 ebx, ecx, edx, eax = 1;
ctxt->opt->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
if (!(ecx & FFL(MWAIT)))
return emulate_ud(ctxt);

and also in em_mwait.

> +
> + if (ctxt->mode != X86EMUL_MODE_PROT64)
> + rcx = (u32)rcx;
> + if (rcx != 0)
> + return emulate_gp(ctxt, 0);
> +
> + addr.seg = seg_override(ctxt);
> + addr.ea = ctxt->ad_bytes == 8 ? rax : (u32)rax;
> + rc = segmented_read(ctxt, addr, &byte, 1);
> + if (rc != X86EMUL_CONTINUE)
> + return rc;
> +
> + printk_once(KERN_WARNING "kvm: MONITOR instruction emulated as NOP!\n");
> + return X86EMUL_CONTINUE;
> +}
> +
> +static int em_mwait(struct x86_emulate_ctxt *ctxt)
> +{
> + u64 rcx = reg_read(ctxt, VCPU_REGS_RCX);
> +
> + if (ctxt->mode != X86EMUL_MODE_PROT64)
> + rcx = (u32)rcx;
> + if ((rcx & ~1UL) != 0)
> + return emulate_gp(ctxt, 0);
> +
> + /* Accepting interrupt as break event regardless to cpuid */
> + printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
> + return X86EMUL_CONTINUE;
> +}
> +
> static bool valid_cr(int nr)
> {
> switch (nr) {
> @@ -3557,8 +3594,8 @@ static int check_perm_out(struct x86_emulate_ctxt *ctxt)
> F2bv(((_f) & ~Lock) | DstAcc | SrcImm, _e)
>
> static const struct opcode group7_rm1[] = {
> - DI(SrcNone | Priv, monitor),
> - DI(SrcNone | Priv, mwait),
> + II(SrcNone | Priv | NoBigReal | UDOnPriv, em_monitor, monitor),
> + II(SrcNone | Priv | NoBigReal | UDOnPriv, em_mwait, mwait),
> N, N, N, N, N, N,
> };
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index ec8366c..a524e04 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3274,24 +3274,6 @@ static int pause_interception(struct vcpu_svm *svm)
> return 1;
> }
>
> -static int nop_interception(struct vcpu_svm *svm)
> -{
> - skip_emulated_instruction(&(svm->vcpu));
> - return 1;
> -}
> -
> -static int monitor_interception(struct vcpu_svm *svm)
> -{
> - printk_once(KERN_WARNING "kvm: MONITOR instruction emulated as NOP!\n");
> - return nop_interception(svm);
> -}
> -
> -static int mwait_interception(struct vcpu_svm *svm)
> -{
> - printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
> - return nop_interception(svm);
> -}
> -
> static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
> [SVM_EXIT_READ_CR0] = cr_interception,
> [SVM_EXIT_READ_CR3] = cr_interception,
> @@ -3349,8 +3331,8 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
> [SVM_EXIT_CLGI] = clgi_interception,
> [SVM_EXIT_SKINIT] = skinit_interception,
> [SVM_EXIT_WBINVD] = emulate_on_interception,
> - [SVM_EXIT_MONITOR] = monitor_interception,
> - [SVM_EXIT_MWAIT] = mwait_interception,
> + [SVM_EXIT_MONITOR] = emulate_on_interception,
> + [SVM_EXIT_MWAIT] = emulate_on_interception,
> [SVM_EXIT_XSETBV] = xsetbv_interception,
> [SVM_EXIT_NPF] = pf_interception,
> };
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 801332e..7023e71 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5672,22 +5672,17 @@ static int handle_pause(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> -static int handle_nop(struct kvm_vcpu *vcpu)
> +static int handle_emulate(struct kvm_vcpu *vcpu)
> {
> - skip_emulated_instruction(vcpu);
> - return 1;
> -}
> + int err = emulate_instruction(vcpu, 0);
>
> -static int handle_mwait(struct kvm_vcpu *vcpu)
> -{
> - printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
> - return handle_nop(vcpu);
> -}
> -
> -static int handle_monitor(struct kvm_vcpu *vcpu)
> -{
> - printk_once(KERN_WARNING "kvm: MONITOR instruction emulated as NOP!\n");
> - return handle_nop(vcpu);
> + if (err != EMULATE_DONE) {
> + vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> + vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
> + vcpu->run->internal.ndata = 0;
> + return 0;
> + }
> + return 1;
> }
>
> /*
> @@ -6651,8 +6646,8 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
> [EXIT_REASON_EPT_VIOLATION] = handle_ept_violation,
> [EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig,
> [EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause,
> - [EXIT_REASON_MWAIT_INSTRUCTION] = handle_mwait,
> - [EXIT_REASON_MONITOR_INSTRUCTION] = handle_monitor,
> + [EXIT_REASON_MWAIT_INSTRUCTION] = handle_emulate,
> + [EXIT_REASON_MONITOR_INSTRUCTION] = handle_emulate,
> [EXIT_REASON_INVEPT] = handle_invept,
> };
>
> --
> 1.9.1
>
> --
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