[01/15] KVM: VMX: Do not adverise RDPID if ENABLE_RDTSCP control is unsupported
diff mbox series

Message ID 20210504171734.1434054-2-seanjc@google.com
State New, archived
Headers show
Series
  • KVM: x86: RDPID/RDTSCP fixes and uret MSR cleanups
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Commit Message

Sean Christopherson May 4, 2021, 5:17 p.m. UTC
Clear KVM's RDPID capability if the ENABLE_RDTSCP secondary exec control is
unsupported.  Despite being enumerated in a separate CPUID flag, RDPID is
bundled under the same VMCS control as RDTSCP and will #UD in VMX non-root
if ENABLE_RDTSCP is not enabled.

Fixes: 41cd02c6f7f6 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Jim Mattson May 4, 2021, 5:37 p.m. UTC | #1
On Tue, May 4, 2021 at 10:17 AM Sean Christopherson <seanjc@google.com> wrote:
>
> Clear KVM's RDPID capability if the ENABLE_RDTSCP secondary exec control is
> unsupported.  Despite being enumerated in a separate CPUID flag, RDPID is
> bundled under the same VMCS control as RDTSCP and will #UD in VMX non-root
> if ENABLE_RDTSCP is not enabled.
>
> Fixes: 41cd02c6f7f6 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>

But KVM will happily emulate RDPID if the instruction causes a #UD
VM-exit, won't it? See commit fb6d4d340e05 (KVM: x86: emulate RDPID).
Jim Mattson May 4, 2021, 5:53 p.m. UTC | #2
On Tue, May 4, 2021 at 10:37 AM Jim Mattson <jmattson@google.com> wrote:
>
> On Tue, May 4, 2021 at 10:17 AM Sean Christopherson <seanjc@google.com> wrote:
> >
> > Clear KVM's RDPID capability if the ENABLE_RDTSCP secondary exec control is
> > unsupported.  Despite being enumerated in a separate CPUID flag, RDPID is
> > bundled under the same VMCS control as RDTSCP and will #UD in VMX non-root
> > if ENABLE_RDTSCP is not enabled.
> >
> > Fixes: 41cd02c6f7f6 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
>
> But KVM will happily emulate RDPID if the instruction causes a #UD
> VM-exit, won't it? See commit fb6d4d340e05 (KVM: x86: emulate RDPID).

Oh, after reading the second patch, I now see why this is needed.

You mispelled 'advertise' in the summary line.

Reviewed-by: Jim Mattson <jmattson@google.com>
Sean Christopherson May 4, 2021, 6:14 p.m. UTC | #3
On Tue, May 04, 2021, Jim Mattson wrote:
> On Tue, May 4, 2021 at 10:37 AM Jim Mattson <jmattson@google.com> wrote:
> >
> > On Tue, May 4, 2021 at 10:17 AM Sean Christopherson <seanjc@google.com> wrote:
> > >
> > > Clear KVM's RDPID capability if the ENABLE_RDTSCP secondary exec control is
> > > unsupported.  Despite being enumerated in a separate CPUID flag, RDPID is
> > > bundled under the same VMCS control as RDTSCP and will #UD in VMX non-root
> > > if ENABLE_RDTSCP is not enabled.
> > >
> > > Fixes: 41cd02c6f7f6 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Sean Christopherson <seanjc@google.com>
> >
> > But KVM will happily emulate RDPID if the instruction causes a #UD
> > VM-exit, won't it? See commit fb6d4d340e05 (KVM: x86: emulate RDPID).
> 
> Oh, after reading the second patch, I now see why this is needed.

Yeah.  Technically, once common x86 can query MSR_TSC_AUX support directly at
the end of the series, the emulation enumeration could be:

		if (kvm_is_supported_user_return_msr(MSR_TSC_AUX))
			entry->ecx = F(RDPID);

I think I actually meant to do that, then lost track of that TODO item when
reworking the series for the umpteenth time.

Practically speaking, the only way for kvm_is_supported_user_return_msr() to be
meaningful vs. kvm_cpu_cap_has() is if RDTSCP is supported in hardware but the
VMCS control is not available.  And I suppose there's also the case where
X86_FEATURE_RDTSCP was cleared by the kernel, but I feel like KVM should respect
the kernel's avoidance of RDTSCP/MSR_TSC_AUX in that case.  Regarding the silly
VMCS case, I have no objection to making the change, but I also don't care if we
sweep it under the rug.
Reiji Watanabe May 5, 2021, 3:04 a.m. UTC | #4
On Tue, May 4, 2021 at 10:17 AM Sean Christopherson <seanjc@google.com> wrote:
>
> Clear KVM's RDPID capability if the ENABLE_RDTSCP secondary exec control is
> unsupported.  Despite being enumerated in a separate CPUID flag, RDPID is
> bundled under the same VMCS control as RDTSCP and will #UD in VMX non-root
> if ENABLE_RDTSCP is not enabled.
>
> Fixes: 41cd02c6f7f6 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Reiji Watanabe <reijiw@google.com>
Maxim Levitsky May 10, 2021, 8:03 a.m. UTC | #5
On Tue, 2021-05-04 at 10:17 -0700, Sean Christopherson wrote:
> Clear KVM's RDPID capability if the ENABLE_RDTSCP secondary exec control is
> unsupported.  Despite being enumerated in a separate CPUID flag, RDPID is
> bundled under the same VMCS control as RDTSCP and will #UD in VMX non-root
> if ENABLE_RDTSCP is not enabled.
> 
> Fixes: 41cd02c6f7f6 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 10b610fc7bbc..82404ee2520e 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7377,9 +7377,11 @@ static __init void vmx_set_cpu_caps(void)
>  	if (!cpu_has_vmx_xsaves())
>  		kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
>  
> -	/* CPUID 0x80000001 */
> -	if (!cpu_has_vmx_rdtscp())
> +	/* CPUID 0x80000001 and 0x7 (RDPID) */
> +	if (!cpu_has_vmx_rdtscp()) {
>  		kvm_cpu_cap_clear(X86_FEATURE_RDTSCP);
> +		kvm_cpu_cap_clear(X86_FEATURE_RDPID);
> +	}
>  
>  	if (cpu_has_vmx_waitpkg())
>  		kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky

Patch
diff mbox series

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 10b610fc7bbc..82404ee2520e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7377,9 +7377,11 @@  static __init void vmx_set_cpu_caps(void)
 	if (!cpu_has_vmx_xsaves())
 		kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
 
-	/* CPUID 0x80000001 */
-	if (!cpu_has_vmx_rdtscp())
+	/* CPUID 0x80000001 and 0x7 (RDPID) */
+	if (!cpu_has_vmx_rdtscp()) {
 		kvm_cpu_cap_clear(X86_FEATURE_RDTSCP);
+		kvm_cpu_cap_clear(X86_FEATURE_RDPID);
+	}
 
 	if (cpu_has_vmx_waitpkg())
 		kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);