[PATCH 0/2] Fix issue with not starting nesting guests on my system

[PATCH 0/2] Fix issue with not starting nesting guests on my system

[Maxim Levitsky]

On my AMD machine I noticed that I can't start any nested guests,
because nested KVM (everything from master git branches) complains
that it can't find msr MSR_IA32_UMWAIT_CONTROL which my system doesn't support
at all anyway.

I traced it to the recently added UMWAIT support to qemu and kvm.
The kvm portion exposed the new MSR in KVM_GET_MSR_INDEX_LIST without
checking that it the underlying feature is supported in CPUID.
It happened to work when non nested because as a precation kvm,
tries to read each MSR on host before adding it to that list,
and when read gets a #GP it ignores it.

When running nested, the L1 hypervisor can be set to ignore unknown
msr read/writes (I need this for some other guests), thus this safety
check doesn't work anymore.

V2: * added a patch to setup correctly the X86_FEATURE_WAITPKG kvm capability
    * dropped the cosmetic fix patch as it is now fixed in kvm/queue

Best regards,
	Maxim Levitsky

Maxim Levitsky (2):
  kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities
  kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally

 arch/x86/kvm/vmx/vmx.c | 3 +++
 arch/x86/kvm/x86.c     | 4 ++++
 2 files changed, 7 insertions(+)

-- 
2.26.2

[PATCH 1/2] kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities

[Maxim Levitsky]

Even though we might not allow the guest to use
WAITPKG's new instructions, we should tell KVM
that the feature is supported by the host CPU.

Note that vmx_waitpkg_supported checks that WAITPKG
_can_ be set in secondary execution controls as specified
by VMX capability MSR, rather that we actually enable it for a guest.

Fixes: e69e72faa3a0 KVM: x86: Add support for user wait instructions

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/x86/kvm/vmx/vmx.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 55712dd86bafa..fca493d4517c5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7298,6 +7298,9 @@ static __init void vmx_set_cpu_caps(void)
 	/* CPUID 0x80000001 */
 	if (!cpu_has_vmx_rdtscp())
 		kvm_cpu_cap_clear(X86_FEATURE_RDTSCP);
+
+	if (vmx_waitpkg_supported())
+		kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);
 }
 
 static void vmx_request_immediate_exit(struct kvm_vcpu *vcpu)
-- 
2.26.2

Re: [PATCH 1/2] kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities

[Sean Christopherson]

On Sat, May 23, 2020 at 07:14:54PM +0300, Maxim Levitsky wrote:
> Even though we might not allow the guest to use
> WAITPKG's new instructions, we should tell KVM
> that the feature is supported by the host CPU.
> 
> Note that vmx_waitpkg_supported checks that WAITPKG
> _can_ be set in secondary execution controls as specified
> by VMX capability MSR, rather that we actually enable it for a guest.

These line wraps are quite weird and inconsistent.

> 
> Fixes: e69e72faa3a0 KVM: x86: Add support for user wait instructions

Checkpatch doesn't complain,  but the preferred Fixes format is

  Fixes: e69e72faa3a07 ("KVM: x86: Add support for user wait instructions")

e.g.

  git show -s --pretty='tformat:%h ("%s")'

For the code itself:

Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>

> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 55712dd86bafa..fca493d4517c5 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7298,6 +7298,9 @@ static __init void vmx_set_cpu_caps(void)
>  	/* CPUID 0x80000001 */
>  	if (!cpu_has_vmx_rdtscp())
>  		kvm_cpu_cap_clear(X86_FEATURE_RDTSCP);
> +
> +	if (vmx_waitpkg_supported())
> +		kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);
>  }
>  
>  static void vmx_request_immediate_exit(struct kvm_vcpu *vcpu)
> -- 
> 2.26.2
> 

Re: [PATCH 1/2] kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities

[Maxim Levitsky]

On Tue, 2020-05-26 at 18:20 -0700, Sean Christopherson wrote:
> On Sat, May 23, 2020 at 07:14:54PM +0300, Maxim Levitsky wrote:
> > Even though we might not allow the guest to use
> > WAITPKG's new instructions, we should tell KVM
> > that the feature is supported by the host CPU.
> > 
> > Note that vmx_waitpkg_supported checks that WAITPKG
> > _can_ be set in secondary execution controls as specified
> > by VMX capability MSR, rather that we actually enable it for a
> > guest.
> 
> These line wraps are quite weird and inconsistent.
Known issue for me, I usually don't have line wrapping enabled,
and I wrap the lines a bit earlier that 72 character limit. 
I'll re-formatted the commit message to be on 72 line format and I will
try now to pay much more attention to that.

> 
> > Fixes: e69e72faa3a0 KVM: x86: Add support for user wait
> > instructions
> 
> Checkpatch doesn't complain,  but the preferred Fixes format is
> 
>   Fixes: e69e72faa3a07 ("KVM: x86: Add support for user wait
> instructions")


> 
> e.g.
> 
>   git show -s --pretty='tformat:%h ("%s")'

Got it, and added to git aliases :-)

> 
> For the code itself:
> 
> Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Thank you!

> 
> > Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> >  arch/x86/kvm/vmx/vmx.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 55712dd86bafa..fca493d4517c5 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -7298,6 +7298,9 @@ static __init void vmx_set_cpu_caps(void)
> >  	/* CPUID 0x80000001 */
> >  	if (!cpu_has_vmx_rdtscp())
> >  		kvm_cpu_cap_clear(X86_FEATURE_RDTSCP);
> > +
> > +	if (vmx_waitpkg_supported())
> > +		kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);
> >  }
> >  
> >  static void vmx_request_immediate_exit(struct kvm_vcpu *vcpu)
> > -- 
> > 2.26.2
> > 

[PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally

[Maxim Levitsky]

This msr is only available when the host supports WAITPKG feature.

This breaks a nested guest, if the L1 hypervisor is set to ignore
unknown msrs, because the only other safety check that the
kernel does is that it attempts to read the msr and
rejects it if it gets an exception.

Fixes: 6e3ba4abce KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/x86/kvm/x86.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b226fb8abe41b..4752293312947 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5316,6 +5316,10 @@ static void kvm_init_msr_list(void)
 			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
 				continue;
 			break;
+		case MSR_IA32_UMWAIT_CONTROL:
+			if (!kvm_cpu_cap_has(X86_FEATURE_WAITPKG))
+				continue;
+			break;
 		default:
 			break;
 		}
-- 
2.26.2

Re: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally

[Sean Christopherson]

On Sat, May 23, 2020 at 07:14:55PM +0300, Maxim Levitsky wrote:
> This msr is only available when the host supports WAITPKG feature.
> 
> This breaks a nested guest, if the L1 hypervisor is set to ignore
> unknown msrs, because the only other safety check that the
> kernel does is that it attempts to read the msr and
> rejects it if it gets an exception.
> 
> Fixes: 6e3ba4abce KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

Same comments on the line wraps and Fixes tag.

For the code:

Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>

> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  arch/x86/kvm/x86.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b226fb8abe41b..4752293312947 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5316,6 +5316,10 @@ static void kvm_init_msr_list(void)
>  			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
>  				continue;
>  			break;
> +		case MSR_IA32_UMWAIT_CONTROL:
> +			if (!kvm_cpu_cap_has(X86_FEATURE_WAITPKG))
> +				continue;
> +			break;
>  		default:
>  			break;
>  		}
> -- 
> 2.26.2
> 

Re: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally

[Maxim Levitsky]

On Tue, 2020-05-26 at 18:21 -0700, Sean Christopherson wrote:
> On Sat, May 23, 2020 at 07:14:55PM +0300, Maxim Levitsky wrote:
> > This msr is only available when the host supports WAITPKG feature.
> > 
> > This breaks a nested guest, if the L1 hypervisor is set to ignore
> > unknown msrs, because the only other safety check that the
> > kernel does is that it attempts to read the msr and
> > rejects it if it gets an exception.
> > 
> > Fixes: 6e3ba4abce KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL
> 
> Same comments on the line wraps and Fixes tag.
I rewrote the commit message and I hope that the new version
is better. I fixed the 'fixes' message as well.

> 
> For the code:
> 
> Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Thank you!

Best regards,
	Maxim Levitsky


> 
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> >  arch/x86/kvm/x86.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index b226fb8abe41b..4752293312947 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -5316,6 +5316,10 @@ static void kvm_init_msr_list(void)
> >  			    min(INTEL_PMC_MAX_GENERIC,
> > x86_pmu.num_counters_gp))
> >  				continue;
> >  			break;
> > +		case MSR_IA32_UMWAIT_CONTROL:
> > +			if (!kvm_cpu_cap_has(X86_FEATURE_WAITPKG))
> > +				continue;
> > +			break;
> >  		default:
> >  			break;
> >  		}
> > -- 
> > 2.26.2
> > 

Re: [PATCH 0/2] Fix issue with not starting nesting guests on my system

[Krish Sadhukhan]

On 5/23/20 9:14 AM, Maxim Levitsky wrote:
> On my AMD machine I noticed that I can't start any nested guests,
> because nested KVM (everything from master git branches) complains
> that it can't find msr MSR_IA32_UMWAIT_CONTROL which my system doesn't support
> at all anyway.
>
> I traced it to the recently added UMWAIT support to qemu and kvm.
> The kvm portion exposed the new MSR in KVM_GET_MSR_INDEX_LIST without
> checking that it the underlying feature is supported in CPUID.
> It happened to work when non nested because as a precation kvm,
> tries to read each MSR on host before adding it to that list,
> and when read gets a #GP it ignores it.
>
> When running nested, the L1 hypervisor can be set to ignore unknown
> msr read/writes (I need this for some other guests), thus this safety
> check doesn't work anymore.
>
> V2: * added a patch to setup correctly the X86_FEATURE_WAITPKG kvm capability
>      * dropped the cosmetic fix patch as it is now fixed in kvm/queue
>
> Best regards,
> 	Maxim Levitsky
>
> Maxim Levitsky (2):
>    kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities
>    kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally
>
>   arch/x86/kvm/vmx/vmx.c | 3 +++
>   arch/x86/kvm/x86.c     | 4 ++++
>   2 files changed, 7 insertions(+)
>
Nit: The added 'break' statement in patch# 2 is not required.

Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>

Re: [PATCH 0/2] Fix issue with not starting nesting guests on my system

[Sean Christopherson]

On Tue, May 26, 2020 at 06:03:32PM -0700, Krish Sadhukhan wrote:
> 
> On 5/23/20 9:14 AM, Maxim Levitsky wrote:
> >On my AMD machine I noticed that I can't start any nested guests,
> >because nested KVM (everything from master git branches) complains
> >that it can't find msr MSR_IA32_UMWAIT_CONTROL which my system doesn't support
> >at all anyway.
> >
> >I traced it to the recently added UMWAIT support to qemu and kvm.
> >The kvm portion exposed the new MSR in KVM_GET_MSR_INDEX_LIST without
> >checking that it the underlying feature is supported in CPUID.
> >It happened to work when non nested because as a precation kvm,
> >tries to read each MSR on host before adding it to that list,
> >and when read gets a #GP it ignores it.
> >
> >When running nested, the L1 hypervisor can be set to ignore unknown
> >msr read/writes (I need this for some other guests), thus this safety
> >check doesn't work anymore.
> >
> >V2: * added a patch to setup correctly the X86_FEATURE_WAITPKG kvm capability
> >     * dropped the cosmetic fix patch as it is now fixed in kvm/queue
> >
> >Best regards,
> >	Maxim Levitsky
> >
> >Maxim Levitsky (2):
> >   kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities
> >   kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally
> >
> >  arch/x86/kvm/vmx/vmx.c | 3 +++
> >  arch/x86/kvm/x86.c     | 4 ++++
> >  2 files changed, 7 insertions(+)
> >
> Nit: The added 'break' statement in patch# 2 is not required.

It is unless you want to add a fallthrough annotation.

Re: [PATCH 0/2] Fix issue with not starting nesting guests on my system

[Sean Christopherson]

On Sat, May 23, 2020 at 07:14:53PM +0300, Maxim Levitsky wrote:
> On my AMD machine I noticed that I can't start any nested guests,
> because nested KVM (everything from master git branches) complains
> that it can't find msr MSR_IA32_UMWAIT_CONTROL which my system doesn't support
> at all anyway.
> 
> I traced it to the recently added UMWAIT support to qemu and kvm.
> The kvm portion exposed the new MSR in KVM_GET_MSR_INDEX_LIST without
> checking that it the underlying feature is supported in CPUID.
> It happened to work when non nested because as a precation kvm,
> tries to read each MSR on host before adding it to that list,
> and when read gets a #GP it ignores it.
> 
> When running nested, the L1 hypervisor can be set to ignore unknown
> msr read/writes (I need this for some other guests), thus this safety
> check doesn't work anymore.
> 
> V2: * added a patch to setup correctly the X86_FEATURE_WAITPKG kvm capability
>     * dropped the cosmetic fix patch as it is now fixed in kvm/queue
> 
> Best regards,
> 	Maxim Levitsky
> 
> Maxim Levitsky (2):
>   kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities
>   kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally

Standard scoping in the shortlog is "KVM: VMX:" and "KVM: x86:".

> 
>  arch/x86/kvm/vmx/vmx.c | 3 +++
>  arch/x86/kvm/x86.c     | 4 ++++
>  2 files changed, 7 insertions(+)
> 
> -- 
> 2.26.2
> 
> 

Re: [PATCH 0/2] Fix issue with not starting nesting guests on my system

[Maxim Levitsky]

On Tue, 2020-05-26 at 18:13 -0700, Sean Christopherson wrote:
> On Sat, May 23, 2020 at 07:14:53PM +0300, Maxim Levitsky wrote:
> > On my AMD machine I noticed that I can't start any nested guests,
> > because nested KVM (everything from master git branches) complains
> > that it can't find msr MSR_IA32_UMWAIT_CONTROL which my system
> > doesn't support
> > at all anyway.
> > 
> > I traced it to the recently added UMWAIT support to qemu and kvm.
> > The kvm portion exposed the new MSR in KVM_GET_MSR_INDEX_LIST
> > without
> > checking that it the underlying feature is supported in CPUID.
> > It happened to work when non nested because as a precation kvm,
> > tries to read each MSR on host before adding it to that list,
> > and when read gets a #GP it ignores it.
> > 
> > When running nested, the L1 hypervisor can be set to ignore unknown
> > msr read/writes (I need this for some other guests), thus this
> > safety
> > check doesn't work anymore.
> > 
> > V2: * added a patch to setup correctly the X86_FEATURE_WAITPKG kvm
> > capability
> >     * dropped the cosmetic fix patch as it is now fixed in
> > kvm/queue
> > 
> > Best regards,
> > 	Maxim Levitsky
> > 
> > Maxim Levitsky (2):
> >   kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities
> >   kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally
> 
> Standard scoping in the shortlog is "KVM: VMX:" and "KVM: x86:".
This another thing I usually mess up in the commit messages.
Fixed and noted for futher patches 

> 
> >  arch/x86/kvm/vmx/vmx.c | 3 +++
> >  arch/x86/kvm/x86.c     | 4 ++++
> >  2 files changed, 7 insertions(+)
> > 
> > -- 
> > 2.26.2
> > 
> > 

Re: [PATCH 0/2] Fix issue with not starting nesting guests on my system

[Maxim Levitsky]

On Tue, 2020-05-26 at 18:13 -0700, Sean Christopherson wrote:
> On Sat, May 23, 2020 at 07:14:53PM +0300, Maxim Levitsky wrote:
> > On my AMD machine I noticed that I can't start any nested guests,
> > because nested KVM (everything from master git branches) complains
> > that it can't find msr MSR_IA32_UMWAIT_CONTROL which my system
> > doesn't support
> > at all anyway.
> > 
> > I traced it to the recently added UMWAIT support to qemu and kvm.
> > The kvm portion exposed the new MSR in KVM_GET_MSR_INDEX_LIST
> > without
> > checking that it the underlying feature is supported in CPUID.
> > It happened to work when non nested because as a precation kvm,
> > tries to read each MSR on host before adding it to that list,
> > and when read gets a #GP it ignores it.
> > 
> > When running nested, the L1 hypervisor can be set to ignore unknown
> > msr read/writes (I need this for some other guests), thus this
> > safety
> > check doesn't work anymore.
> > 
> > V2: * added a patch to setup correctly the X86_FEATURE_WAITPKG kvm
> > capability
> >     * dropped the cosmetic fix patch as it is now fixed in kvm/queue
> > 
> > Best regards,
> > 	Maxim Levitsky
> > 
> > Maxim Levitsky (2):
> >   kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities
> >   kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally
> 
> Standard scoping in the shortlog is "KVM: VMX:" and "KVM: x86:".
Noted and I will use it from now on.
Thanks!

Best regards,
	Maxim Levitsky

> 
> >  arch/x86/kvm/vmx/vmx.c | 3 +++
> >  arch/x86/kvm/x86.c     | 4 ++++
> >  2 files changed, 7 insertions(+)
> > 
> > -- 
> > 2.26.2
> > 
> > 

Re: [PATCH 0/2] Fix issue with not starting nesting guests on my system

[Paolo Bonzini]

On 23/05/20 18:14, Maxim Levitsky wrote:
> On my AMD machine I noticed that I can't start any nested guests,
> because nested KVM (everything from master git branches) complains
> that it can't find msr MSR_IA32_UMWAIT_CONTROL which my system doesn't support
> at all anyway.
> 
> I traced it to the recently added UMWAIT support to qemu and kvm.
> The kvm portion exposed the new MSR in KVM_GET_MSR_INDEX_LIST without
> checking that it the underlying feature is supported in CPUID.
> It happened to work when non nested because as a precation kvm,
> tries to read each MSR on host before adding it to that list,
> and when read gets a #GP it ignores it.
> 
> When running nested, the L1 hypervisor can be set to ignore unknown
> msr read/writes (I need this for some other guests), thus this safety
> check doesn't work anymore.
> 
> V2: * added a patch to setup correctly the X86_FEATURE_WAITPKG kvm capability
>     * dropped the cosmetic fix patch as it is now fixed in kvm/queue
> 
> Best regards,
> 	Maxim Levitsky
> 
> Maxim Levitsky (2):
>   kvm/x86/vmx: enable X86_FEATURE_WAITPKG in KVM capabilities
>   kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally
> 
>  arch/x86/kvm/vmx/vmx.c | 3 +++
>  arch/x86/kvm/x86.c     | 4 ++++
>  2 files changed, 7 insertions(+)
> 

Queued for 5.7, thanks (with cosmetic touches to the commit message, and
moving the "case" earlier to avoid conflicts).

Paolo