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From: "Tian, Kevin" <kevin.tian@intel.com>
To: "Christopherson,, Sean" <seanjc@google.com>,
	"Zhong, Yang" <yang.zhong@intel.com>
Cc: "x86@kernel.org" <x86@kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-kselftest@vger.kernel.org"
	<linux-kselftest@vger.kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"bp@alien8.de" <bp@alien8.de>,
	"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	"corbet@lwn.net" <corbet@lwn.net>,
	"shuah@kernel.org" <shuah@kernel.org>,
	"Nakajima, Jun" <jun.nakajima@intel.com>,
	"jing2.liu@linux.intel.com" <jing2.liu@linux.intel.com>,
	"Liu, Jing2" <jing2.liu@intel.com>,
	"Zeng, Guang" <guang.zeng@intel.com>,
	"Wang, Wei W" <wei.w.wang@intel.com>
Subject: RE: [PATCH v4 10/21] kvm: x86: Add emulation for IA32_XFD
Date: Wed, 5 Jan 2022 00:22:25 +0000	[thread overview]
Message-ID: <BN9PR11MB52766D60A78E5C736E1BD4FB8C4B9@BN9PR11MB5276.namprd11.prod.outlook.com> (raw)
In-Reply-To: <YdSgzsiBft/NgxdF@google.com>

> From: Sean Christopherson <seanjc@google.com>
> Sent: Wednesday, January 5, 2022 3:33 AM
> 
> On Wed, Dec 29, 2021, Yang Zhong wrote:
> > From: Jing Liu <jing2.liu@intel.com>
> >
> > Intel's eXtended Feature Disable (XFD) feature allows the software
> > to dynamically adjust fpstate buffer size for XSAVE features which
> > have large state.
> >
> > Because fpstate has been expanded for all possible dynamic xstates
> > at KVM_SET_CPUID2, emulation of the IA32_XFD MSR is straightforward.
> > For write just call fpu_update_guest_xfd() to update the guest fpu
> > container once all the sanity checks are passed. For read then
> > return the cached value in the container.
> >
> > Signed-off-by: Zeng Guang <guang.zeng@intel.com>
> > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> > Signed-off-by: Jing Liu <jing2.liu@intel.com>
> > Signed-off-by: Yang Zhong <yang.zhong@intel.com>
> > ---
> >  arch/x86/kvm/x86.c | 27 +++++++++++++++++++++++++++
> >  1 file changed, 27 insertions(+)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index e50e97ac4408..36677b754ac9 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1359,6 +1359,7 @@ static const u32 msrs_to_save_all[] = {
> >  	MSR_F15H_PERF_CTL3, MSR_F15H_PERF_CTL4,
> MSR_F15H_PERF_CTL5,
> >  	MSR_F15H_PERF_CTR0, MSR_F15H_PERF_CTR1,
> MSR_F15H_PERF_CTR2,
> >  	MSR_F15H_PERF_CTR3, MSR_F15H_PERF_CTR4,
> MSR_F15H_PERF_CTR5,
> > +	MSR_IA32_XFD,
> >  };
> >
> >  static u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_all)];
> > @@ -3669,6 +3670,19 @@ int kvm_set_msr_common(struct kvm_vcpu
> *vcpu, struct msr_data *msr_info)
> >  			return 1;
> >  		vcpu->arch.msr_misc_features_enables = data;
> >  		break;
> > +#ifdef CONFIG_X86_64
> > +	case MSR_IA32_XFD:
> > +		if (!msr_info->host_initiated &&
> > +		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
> > +			return 1;
> > +
> > +		if (data & ~(XFEATURE_MASK_USER_DYNAMIC &
> > +			     vcpu->arch.guest_supported_xcr0))
> > +			return 1;
> > +
> > +		fpu_update_guest_xfd(&vcpu->arch.guest_fpu, data);
> > +		break;
> > +#endif
> >  	default:
> >  		if (kvm_pmu_is_valid_msr(vcpu, msr))
> >  			return kvm_pmu_set_msr(vcpu, msr_info);
> > @@ -3989,6 +4003,15 @@ int kvm_get_msr_common(struct kvm_vcpu
> *vcpu, struct msr_data *msr_info)
> >  	case MSR_K7_HWCR:
> >  		msr_info->data = vcpu->arch.msr_hwcr;
> >  		break;
> > +#ifdef CONFIG_X86_64
> > +	case MSR_IA32_XFD:
> > +		if (!msr_info->host_initiated &&
> > +		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
> > +			return 1;
> > +
> > +		msr_info->data = vcpu->arch.guest_fpu.fpstate->xfd;
> > +		break;
> > +#endif
> >  	default:
> >  		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
> >  			return kvm_pmu_get_msr(vcpu, msr_info);
> > @@ -6422,6 +6445,10 @@ static void kvm_init_msr_list(void)
> >  			    min(INTEL_PMC_MAX_GENERIC,
> x86_pmu.num_counters_gp))
> >  				continue;
> >  			break;
> > +		case MSR_IA32_XFD:
> > +			if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
> > +				continue;
> 
> I suspect the 32-bit host support is wrong.  The kernel's handle_xfd_event()
> checks for 64-bit support in addition to the CPU feature itself, which implies
> that the feature can be reported in boot_cpu_data for 32-bit kernels.
> 
>   static bool handle_xfd_event(struct pt_regs *regs)
>   {
> 	u64 xfd_err;
> 	int err;
> 
> 	if (!IS_ENABLED(CONFIG_X86_64)
> || !cpu_feature_enabled(X86_FEATURE_XFD))
> 		return false;
> 
> 	...
>   }
> 
> In this specific case, that means KVM will tell userspace it needs to mgirate
> MSR_IA32_XFD, and then reject attempts to read/write the MSR.
> 
> If 32-bit host kernels do not explicitly suppress X86_FEATURE_XFD, then KVM

I didn't find explicit suppress

> needs
> to do:
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 556555537a18..156ce332d55b 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -455,9 +455,11 @@ void kvm_set_cpu_caps(void)
>  #ifdef CONFIG_X86_64
>         unsigned int f_gbpages = F(GBPAGES);
>         unsigned int f_lm = F(LM);
> +       unsigned int f_xfd = F(XFD);
>  #else
>         unsigned int f_gbpages = 0;
>         unsigned int f_lm = 0;
> +       unsigned int f_xfd = 0;
>  #endif
>         memset(kvm_cpu_caps, 0, sizeof(kvm_cpu_caps));
> 
> @@ -545,7 +547,7 @@ void kvm_set_cpu_caps(void)
>         );
> 
>         kvm_cpu_cap_mask(CPUID_D_1_EAX,
> -               F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | F(XSAVES) | F(XFD)
> +               F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | F(XSAVES) | f_xfd
>         );
> 
>         kvm_cpu_cap_init_scattered(CPUID_12_EAX,
> 

so this change makes sense. will incorporate it in next version.

Thanks
Kevin

  reply	other threads:[~2022-01-05  0:22 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-29 13:13 [PATCH v4 00/21] AMX Support in KVM Yang Zhong
2021-12-29 13:13 ` [PATCH v4 01/21] x86/fpu: Extend fpu_xstate_prctl() with guest permissions Yang Zhong
2021-12-29 13:13 ` [PATCH v4 02/21] x86/fpu: Prepare guest FPU for dynamically enabled FPU features Yang Zhong
2021-12-29 13:13 ` [PATCH v4 03/21] kvm: x86: Fix xstate_required_size() to follow XSTATE alignment rule Yang Zhong
2022-01-04 19:54   ` Sean Christopherson
2021-12-29 13:13 ` [PATCH v4 04/21] kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID Yang Zhong
2021-12-29 13:13 ` [PATCH v4 05/21] x86/fpu: Make XFD initialization in __fpstate_reset() a function argument Yang Zhong
2021-12-29 13:13 ` [PATCH v4 06/21] x86/fpu: Add guest support to xfd_enable_feature() Yang Zhong
2021-12-29 13:13 ` [PATCH v4 07/21] x86/fpu: Provide fpu_update_guest_perm_features() for guest Yang Zhong
2021-12-29 13:13 ` [PATCH v4 08/21] kvm: x86: Check and enable permitted dynamic xfeatures at KVM_SET_CPUID2 Yang Zhong
2021-12-29 16:55   ` Sean Christopherson
2021-12-30  2:28     ` Tian, Kevin
2021-12-29 13:13 ` [PATCH v4 09/21] x86/fpu: Provide fpu_update_guest_xfd() for IA32_XFD emulation Yang Zhong
2021-12-29 13:13 ` [PATCH v4 10/21] kvm: x86: Add emulation for IA32_XFD Yang Zhong
2022-01-04 19:32   ` Sean Christopherson
2022-01-05  0:22     ` Tian, Kevin [this message]
2021-12-29 13:13 ` [PATCH v4 11/21] x86/fpu: Prepare xfd_err in struct fpu_guest Yang Zhong
2021-12-29 13:13 ` [PATCH v4 12/21] kvm: x86: Intercept #NM for saving IA32_XFD_ERR Yang Zhong
2022-01-04 20:01   ` Sean Christopherson
2022-01-05  0:27     ` Tian, Kevin
2021-12-29 13:13 ` [PATCH v4 13/21] kvm: x86: Emulate IA32_XFD_ERR for guest Yang Zhong
2021-12-29 13:13 ` [PATCH v4 14/21] kvm: x86: Disable RDMSR interception of IA32_XFD_ERR Yang Zhong
2022-01-04 19:34   ` Sean Christopherson
2022-01-05  0:23     ` Tian, Kevin
2021-12-29 13:13 ` [PATCH v4 15/21] kvm: x86: Add XCR0 support for Intel AMX Yang Zhong
2021-12-29 13:13 ` [PATCH v4 16/21] kvm: x86: Add CPUID " Yang Zhong
2021-12-29 13:13 ` [PATCH v4 17/21] x86/fpu: Add uabi_size to guest_fpu Yang Zhong
2021-12-29 13:13 ` [PATCH v4 18/21] kvm: x86: Add support for getting/setting expanded xstate buffer Yang Zhong
2022-01-04 19:46   ` Sean Christopherson
2022-01-04 20:45     ` Paolo Bonzini
2022-01-05  4:03       ` Tian, Kevin
2021-12-29 13:13 ` [PATCH v4 19/21] kvm: selftests: Add support for KVM_CAP_XSAVE2 Yang Zhong
2021-12-29 13:13 ` [PATCH v4 20/21] x86/fpu: Provide fpu_sync_guest_vmexit_xfd_state() Yang Zhong
2021-12-29 13:13 ` [PATCH v4 21/21] kvm: x86: Disable interception for IA32_XFD on demand Yang Zhong
2021-12-30  8:46 ` [PATCH v4 00/21] AMX Support in KVM Tian, Kevin
2022-01-04 18:36 ` Paolo Bonzini
2022-01-04 18:54   ` Sean Christopherson
2022-01-05  0:10     ` Tian, Kevin

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