From: "H. Peter Anvin" <hpa@zytor.com>
To: Borislav Petkov <bp@alien8.de>, Breno Leitao <leitao@debian.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
vlad.wing@gmail.com, security@kernel.org, kernel-team@meta.com
Subject: Re: [PATCH 6.18.y] x86/cpufeatures: Make X86_FEATURE leaf 17 Linux-specific
Date: Thu, 12 Nov 2026 14:13:31 -0800 [thread overview]
Message-ID: <9492bce8-aab7-4982-8a0c-7d736c745e12@zytor.com> (raw)
In-Reply-To: <20261112045703.GAavVHH8KA2yyCU7oc@fat_crate.local>
Still, I have to wonder if it really makes sense to fold these leaves
like this, since they are going to be populated soon. Surely we're not
that short of bits?
-hpa
On 2026-11-11 20:57, Borislav Petkov wrote:
> On Wed, Nov 11, 2026 at 08:06:21AM -0800, Breno Leitao wrote:
>> From: "Borislav Petkov (AMD)" <bp@alien8.de>
>>
>> commit ddde4abaa0ecc8395e0fcfa3e92f65d481890cc8 upstream.
>>
>> That cpuinfo_x86.x86_capability[] element was supposed to mirror CPUID flags
>> from CPUID_0x80000007_EBX but that leaf has still to this day only three bits
>> defined in it. So move those bits to scattered.c and free the capability
>> element for synthetic flags.
>>
>> No functional changes.
>>
>> [ leitao: Required on 6.18.y: the 6.18.61 backport of ae1d2082d93b
>> ("x86/bugs: Adapt SRSO mitigation to Zen6") put BTB_CTX_ISOLATION in
>> word 17, which here still mirrors CPUID 0x80000007 EBX. The flag is
>> then falsely set on Zen3-5, and Zen5 silently loses its guest->host
>> SRSO mitigation. ]
>
> Good catch, dang. That's nasty one.
>
> Thanks!
>
next prev parent reply other threads:[~2026-11-12 22:14 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-11 16:06 Breno Leitao
2026-11-12 4:57 ` Borislav Petkov
2026-11-12 22:13 ` H. Peter Anvin [this message]
2026-11-12 22:23 ` Borislav Petkov
2026-11-12 23:09 ` Thomas Gleixner
2026-11-12 23:33 ` Borislav Petkov
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