linux-kernel - Re: [PATCH v2 2/2] KVM: x86/emulator: Emulate RDPID only if it is enabled in guest

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Date:   Tue, 15 Mar 2022 23:18:11 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Hou Wenlong <houwenlong.hwl@...group.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] KVM: x86/emulator: Emulate RDPID only if it is
 enabled in guest

On 3/7/22 13:26, Hou Wenlong wrote:
> When RDTSCP is supported but RDPID is not supported in host,
> RDPID emulation is available. However, __kvm_get_msr() would
> only fail when RDTSCP/RDPID both are disabled in guest, so
> the emulator wouldn't inject a #UD when RDPID is disabled but
> RDTSCP is enabled in guest.
> 
> Fixes: fb6d4d340e05 ("KVM: x86: emulate RDPID")
> Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> ---
>   arch/x86/kvm/emulate.c     | 4 +++-
>   arch/x86/kvm/kvm_emulate.h | 1 +
>   arch/x86/kvm/x86.c         | 6 ++++++
>   3 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 3497a35bd085..be83c9c8482d 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -3521,8 +3521,10 @@ static int em_rdpid(struct x86_emulate_ctxt *ctxt)
>   {
>   	u64 tsc_aux = 0;
>   
> -	if (ctxt->ops->get_msr(ctxt, MSR_TSC_AUX, &tsc_aux))
> +	if (!ctxt->ops->guest_has_rdpid(ctxt))
>   		return emulate_ud(ctxt);
> +
> +	ctxt->ops->get_msr(ctxt, MSR_TSC_AUX, &tsc_aux);
>   	ctxt->dst.val = tsc_aux;
>   	return X86EMUL_CONTINUE;
>   }
> diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
> index 29ac5a9679e5..1cbd46cf71f9 100644
> --- a/arch/x86/kvm/kvm_emulate.h
> +++ b/arch/x86/kvm/kvm_emulate.h
> @@ -228,6 +228,7 @@ struct x86_emulate_ops {
>   	bool (*guest_has_long_mode)(struct x86_emulate_ctxt *ctxt);
>   	bool (*guest_has_movbe)(struct x86_emulate_ctxt *ctxt);
>   	bool (*guest_has_fxsr)(struct x86_emulate_ctxt *ctxt);
> +	bool (*guest_has_rdpid)(struct x86_emulate_ctxt *ctxt);
>   
>   	void (*set_nmi_mask)(struct x86_emulate_ctxt *ctxt, bool masked);
>   
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 09c5677f4186..44f97038d3e5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7723,6 +7723,11 @@ static bool emulator_guest_has_fxsr(struct x86_emulate_ctxt *ctxt)
>   	return guest_cpuid_has(emul_to_vcpu(ctxt), X86_FEATURE_FXSR);
>   }
>   
> +static bool emulator_guest_has_rdpid(struct x86_emulate_ctxt *ctxt)
> +{
> +	return guest_cpuid_has(emul_to_vcpu(ctxt), X86_FEATURE_RDPID);
> +}
> +
>   static ulong emulator_read_gpr(struct x86_emulate_ctxt *ctxt, unsigned reg)
>   {
>   	return kvm_register_read_raw(emul_to_vcpu(ctxt), reg);
> @@ -7807,6 +7812,7 @@ static const struct x86_emulate_ops emulate_ops = {
>   	.guest_has_long_mode = emulator_guest_has_long_mode,
>   	.guest_has_movbe     = emulator_guest_has_movbe,
>   	.guest_has_fxsr      = emulator_guest_has_fxsr,
> +	.guest_has_rdpid     = emulator_guest_has_rdpid,
>   	.set_nmi_mask        = emulator_set_nmi_mask,
>   	.get_hflags          = emulator_get_hflags,
>   	.exiting_smm         = emulator_exiting_smm,

Queued, thanks.

Would you try replacing the ->guest_has_... callbacks with just one that 
takes an X86_FEATURE_* constant as a second argument?

Paolo