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From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: Aaron Lewis <aaronlewis@google.com>, "Christopherson,,
	Sean" <seanjc@google.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	"jmattson@google.com" <jmattson@google.com>,
	"Thomas Gleixner" <tglx@linutronix.de>, "bp@suse.de" <bp@suse.de>
Subject: Re: [PATCH v2 1/6] KVM: x86: Clear all supported MPX xfeatures if they are not all set
Date: Tue, 10 Jan 2023 10:32:57 -0800	[thread overview]
Message-ID: <c87904cb-ce6d-1cf4-5b58-4d588660e20f@intel.com> (raw)
In-Reply-To: <CAAAPnDHff-2XFdAgKdfTQnG_a4TCVqWN9wxEhUtiOfiOVMuRWA@mail.gmail.com>

On 1/10/2023 6:49 AM, Aaron Lewis wrote:
> 
> When I run xcr0_cpuid_test it fails because
> xstate_get_guest_group_perm() reports partial support on SPR.  It's
> reporting 0x206e7 rather than the 0x6e7 I was hoping for.  That's why
> I went down the road of sanitizing xcr0.  Though, if it's expected for
> that to report something valid then sanitizing seems like the wrong
> approach.  If xcr0 is invalid it should stay invalid, and it should
> cause a test to fail.

FWIW, we have this [1]:

/* Features which are dynamically enabled for a process on request */
#define XFEATURE_MASK_USER_DYNAMIC	XFEATURE_MASK_XTILE_DATA

IOW, TILE_CFG is not part of the dynamic state. Because this state is 
not XFD-supported, we can't enforce the state use. SDM has relevant text 
here [2]:

"LDTILECFG and TILERELEASE initialize the TILEDATA state component. An 
execution of either of these instructions does not generate #NM when 
XCR0[18] = IA32_XFD[18] = 1; instead, it initializes TILEDATA normally.
(Note that STTILECFG does not use the TILEDATA state component. Thus, an 
execution of this instruction does
not generate #NM when XCR0[18] = IA32_XFD[18] = 1.)"

> Looking at how xstate_get_guest_group_perm() comes through with
> invalid bits I came across this commit:
> 
> 2308ee57d93d ("x86/fpu/amx: Enable the AMX feature in 64-bit mode")
> 
> -       /* [XFEATURE_XTILE_DATA] = XFEATURE_MASK_XTILE, */
> +       [XFEATURE_XTILE_DATA] = XFEATURE_MASK_XTILE_DATA,
> 
> Seems like it should really be:
> 
> +       [XFEATURE_XTILE_DATA] = XFEATURE_MASK_XTILE,

Thus, the change was intentional as far as I can remember.

Thank,
Chang

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/include/asm/fpu/xstate.h#n50
[2] SDM Vol 1. 13.14 Extended Feature Disable (XFD), 
https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html


  reply	other threads:[~2023-01-10 18:39 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-30 16:24 [PATCH v2 0/6] Clean up the supported xfeatures Aaron Lewis
2022-12-30 16:24 ` [PATCH v2 1/6] KVM: x86: Clear all supported MPX xfeatures if they are not all set Aaron Lewis
2023-01-02 15:03   ` Xiaoyao Li
2023-01-03 18:47     ` Sean Christopherson
2023-01-03 18:46   ` Sean Christopherson
2023-01-10 14:49     ` Aaron Lewis
2023-01-10 18:32       ` Chang S. Bae [this message]
2023-01-12 18:21         ` Mingwei Zhang
2023-01-12 18:44           ` Chang S. Bae
2023-01-12 19:17             ` Mingwei Zhang
2023-01-12 20:31               ` Chang S. Bae
2023-01-12 21:21                 ` Mingwei Zhang
2023-01-12 21:33                   ` Chang S. Bae
2023-01-13  0:25                     ` Mingwei Zhang
2023-01-13 14:43                       ` Aaron Lewis
2023-01-17 20:32                         ` Chang S. Bae
2023-01-17 22:39                           ` Mingwei Zhang
2023-01-18  0:34                             ` Chang S. Bae
2022-12-30 16:24 ` [PATCH v2 2/6] KVM: x86: Clear all supported AVX-512 " Aaron Lewis
2023-01-04 16:33   ` Sean Christopherson
2023-01-04 16:39     ` Sean Christopherson
2022-12-30 16:24 ` [PATCH v2 3/6] KVM: x86: Clear all supported AMX " Aaron Lewis
2022-12-30 16:24 ` [PATCH v2 4/6] KVM: selftests: Hoist XGETBV and XSETBV to make them more accessible Aaron Lewis
2022-12-30 16:24 ` [PATCH v2 5/6] KVM: selftests: Add XFEATURE masks to common code Aaron Lewis
2023-01-04 16:43   ` Sean Christopherson
2022-12-30 16:24 ` [PATCH v2 6/6] KVM: selftests: Add XCR0 Test Aaron Lewis
2023-01-04 17:13   ` Sean Christopherson
2023-01-05 22:46     ` Aaron Lewis
2023-01-05 23:10       ` Sean Christopherson

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