Messages in this thread Patch in this message | | | Date | Sun, 23 Jan 2022 14:22:28 +0800 | Subject | Re: [PATCH v6 04/21] kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID | From | Like Xu <> |
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On 8/1/2022 2:54 am, Paolo Bonzini wrote: > From: Jing Liu <jing2.liu@intel.com> > > KVM_GET_SUPPORTED_CPUID should not include any dynamic xstates in > CPUID[0xD] if they have not been requested with prctl. Otherwise > a process which directly passes KVM_GET_SUPPORTED_CPUID to > KVM_SET_CPUID2 would now fail even if it doesn't intend to use a > dynamically enabled feature. Userspace must know that prctl is > required and allocate >4K xstate buffer before setting any dynamic > bit. > > Suggested-by: Paolo Bonzini <pbonzini@redhat.com> > Signed-off-by: Jing Liu <jing2.liu@intel.com> > Signed-off-by: Yang Zhong <yang.zhong@intel.com> > Message-Id: <20220105123532.12586-5-yang.zhong@intel.com> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > Documentation/virt/kvm/api.rst | 4 ++++ > arch/x86/kvm/cpuid.c | 9 ++++++--- > 2 files changed, 10 insertions(+), 3 deletions(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 6b683dfea8f2..f4ea5e41a4d0 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -1687,6 +1687,10 @@ userspace capabilities, and with user requirements (for example, the > user may wish to constrain cpuid to emulate older hardware, or for > feature consistency across a cluster). > > +Dynamically-enabled feature bits need to be requested with > +``arch_prctl()`` before calling this ioctl. Feature bits that have not > +been requested are excluded from the result. > + > Note that certain capabilities, such as KVM_CAP_X86_DISABLE_EXITS, may > expose cpuid features (e.g. MONITOR) which are not supported by kvm in > its default configuration. If userspace enables such capabilities, it > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index f3e6fda6b858..eb52dde5deec 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -815,11 +815,13 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) > goto out; > } > break; > - case 0xd: > - entry->eax &= supported_xcr0; > + case 0xd: { > + u64 guest_perm = xstate_get_guest_group_perm(); > + > + entry->eax &= supported_xcr0 & guest_perm; > entry->ebx = xstate_required_size(supported_xcr0, false);
If we choose to exclude unpermitted xfeatures in the entry->eax, why do we choose to expose the size of unpermitted xfeatures in ebx and ecx?
This seems to be an inconsistency, how about:
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 1bd4d560cbdd..193cbf56a5fa 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -888,12 +888,12 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) } break; case 0xd: { - u64 guest_perm = xstate_get_guest_group_perm(); + u64 supported_xcr0 = supported_xcr0 & xstate_get_guest_group_perm();
- entry->eax &= supported_xcr0 & guest_perm; + entry->eax &= supported_xcr0; entry->ebx = xstate_required_size(supported_xcr0, false); entry->ecx = entry->ebx; - entry->edx &= (supported_xcr0 & guest_perm) >> 32; + entry->edx &= supported_xcr0 >> 32; if (!supported_xcr0) break;
It also helps to fix the CPUID_D_1_EBX and later for (i = 2; i < 64; ++i); Is there anything I've missed ?
> entry->ecx = entry->ebx; > - entry->edx &= supported_xcr0 >> 32; > + entry->edx &= (supported_xcr0 & guest_perm) >> 32; > if (!supported_xcr0) > break; > > @@ -866,6 +868,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function) > entry->edx = 0; > } > break; > + } > case 0x12: > /* Intel SGX */ > if (!kvm_cpu_cap_has(X86_FEATURE_SGX)) {
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