From: Sean Christopherson <seanjc@google.com>
To: Jing Liu <jing2.liu@intel.com>
Cc: x86@kernel.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kselftest@vger.kernel.org, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
pbonzini@redhat.com, corbet@lwn.net, shuah@kernel.org,
jun.nakajima@intel.com, kevin.tian@intel.com,
jing2.liu@linux.intel.com, guang.zeng@intel.com,
wei.w.wang@intel.com, yang.zhong@intel.com
Subject: Re: [PATCH v3 16/22] kvm: x86: Add XCR0 support for Intel AMX
Date: Wed, 29 Dec 2021 00:21:06 +0000 [thread overview]
Message-ID: <Ycup8opdHrjCIy1V@google.com> (raw)
In-Reply-To: <20211222124052.644626-17-jing2.liu@intel.com>
On Wed, Dec 22, 2021, Jing Liu wrote:
> Two XCR0 bits are defined for AMX to support XSAVE mechanism. Bit 17
> is for tilecfg and bit 18 is for tiledata.
>
> The value of XCR0[17:18] is always either 00b or 11b.
Is that an SDM requirement, or an arbitrary Linux/KVM requirement?
> Also, SDM
> recommends that only 64-bit operating systems enable Intel AMX by
> setting XCR0[18:17]. If a 32-bit guest tries to set dynamic bits, it
This is wrong. It has nothing to do with 32-bit guests. The restriction is on
32-bit _host kernels_, which I'm guessing never set the tile bits in _host_ XCR0.
> fails to pass vcpu->arch.guest_supported_xcr0 check and gets a #GP.
>
> Signed-off-by: Yang Zhong <yang.zhong@intel.com>
> Signed-off-by: Jing Liu <jing2.liu@intel.com>
> ---
> arch/x86/kvm/x86.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a48a89f73027..c558c098979a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -210,7 +210,7 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
> #define KVM_SUPPORTED_XCR0 (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
> | XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
> | XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
> - | XFEATURE_MASK_PKRU)
> + | XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
>
> u64 __read_mostly host_efer;
> EXPORT_SYMBOL_GPL(host_efer);
> @@ -990,6 +990,12 @@ static int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
> if ((xcr0 & XFEATURE_MASK_AVX512) != XFEATURE_MASK_AVX512)
> return 1;
> }
> +
> +#ifdef CONFIG_X86_64
Drop the #ifdef, it adds no meaningful value and requires the reader to think
far harder than they should have. Yes, it's technically dead code for 32-bit KVM,
but no one cares about performance of 32-bit KVM, and in any case it's extremely
unlikely this will be anything but noise.
> + if ((xcr0 & XFEATURE_MASK_XTILE) &&
> + ((xcr0 & XFEATURE_MASK_XTILE) != XFEATURE_MASK_XTILE))
> + return 1;
> +#endif
> vcpu->arch.xcr0 = xcr0;
>
> if ((xcr0 ^ old_xcr0) & XFEATURE_MASK_EXTEND)
> --
> 2.27.0
>
next prev parent reply other threads:[~2021-12-29 0:21 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-22 12:40 [PATCH v3 00/22] AMX Support in KVM Jing Liu
2021-12-22 12:40 ` [PATCH v3 01/22] x86/fpu: Extend fpu_xstate_prctl() with guest permissions Jing Liu
2021-12-22 12:40 ` [PATCH v3 02/22] x86/fpu: Prepare guest FPU for dynamically enabled FPU features Jing Liu
2021-12-22 12:40 ` [PATCH v3 03/22] kvm: x86: Fix xstate_required_size() to follow XSTATE alignment rule Jing Liu
2021-12-22 12:40 ` [PATCH v3 04/22] kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID Jing Liu
2021-12-22 12:40 ` [PATCH v3 05/22] kvm: x86: Check permitted dynamic xfeatures at KVM_SET_CPUID2 Jing Liu
2021-12-28 23:38 ` Sean Christopherson
2021-12-29 2:18 ` Tian, Kevin
2021-12-22 12:40 ` [PATCH v3 06/22] x86/fpu: Make XFD initialization in __fpstate_reset() a function argument Jing Liu
2021-12-22 12:40 ` [PATCH v3 07/22] x86/fpu: Add guest support to xfd_enable_feature() Jing Liu
2021-12-22 12:40 ` [PATCH v3 08/22] x86/fpu: Provide fpu_update_guest_perm_features() for guest Jing Liu
2021-12-22 12:40 ` [PATCH v3 09/22] kvm: x86: Enable dynamic XSAVE features at KVM_SET_CPUID2 Jing Liu
2021-12-28 23:54 ` Sean Christopherson
2021-12-29 2:23 ` Tian, Kevin
2021-12-22 12:40 ` [PATCH v3 10/22] x86/fpu: Provide fpu_update_guest_xfd() for IA32_XFD emulation Jing Liu
2021-12-22 12:40 ` [PATCH v3 11/22] kvm: x86: Add emulation for IA32_XFD Jing Liu
2021-12-22 12:40 ` [PATCH v3 12/22] x86/fpu: Prepare xfd_err in struct fpu_guest Jing Liu
2021-12-22 12:40 ` [PATCH v3 13/22] kvm: x86: Intercept #NM for saving IA32_XFD_ERR Jing Liu
2021-12-29 0:09 ` Sean Christopherson
2021-12-29 2:52 ` Tian, Kevin
2021-12-29 17:37 ` Sean Christopherson
2021-12-29 6:50 ` Tian, Kevin
2021-12-29 8:13 ` Tian, Kevin
2021-12-22 12:40 ` [PATCH v3 14/22] kvm: x86: Emulate IA32_XFD_ERR for guest Jing Liu
2021-12-22 12:40 ` [PATCH v3 15/22] kvm: x86: Disable RDMSR interception of IA32_XFD_ERR Jing Liu
2021-12-22 12:40 ` [PATCH v3 16/22] kvm: x86: Add XCR0 support for Intel AMX Jing Liu
2021-12-29 0:21 ` Sean Christopherson [this message]
2021-12-29 3:01 ` Tian, Kevin
2021-12-22 12:40 ` [PATCH v3 17/22] kvm: x86: Add CPUID " Jing Liu
2021-12-22 12:40 ` [PATCH v3 18/22] x86/fpu: Add uabi_size to guest_fpu Jing Liu
2021-12-22 12:40 ` [PATCH v3 19/22] kvm: x86: Get/set expanded xstate buffer Jing Liu
2021-12-29 0:38 ` Sean Christopherson
2021-12-29 2:57 ` Wang, Wei W
2021-12-29 6:36 ` Tian, Kevin
2021-12-22 12:40 ` [PATCH v3 20/22] kvm: selftests: Add support for KVM_CAP_XSAVE2 Jing Liu
2021-12-22 12:40 ` [PATCH v3 21/22] x86/fpu: Provide fpu_sync_guest_vmexit_xfd_state() Jing Liu
2021-12-22 12:40 ` [PATCH v3 22/22] kvm: x86: Disable interception for IA32_XFD on demand Jing Liu
2021-12-29 1:04 ` Sean Christopherson
2021-12-29 3:35 ` Tian, Kevin
2021-12-29 7:16 ` Tian, Kevin
2021-12-29 17:26 ` Sean Christopherson
2021-12-30 1:28 ` Tian, Kevin
2021-12-30 7:04 ` Tian, Kevin
2021-12-31 9:42 ` Tian, Kevin
2021-12-29 7:37 ` Tian, Kevin
2022-01-04 18:32 ` Paolo Bonzini
2022-01-04 18:58 ` Sean Christopherson
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