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Message-ID: <399bbc9d-ae75-4754-8ce9-af563df15a38@intel.com>
Date: Wed, 17 Apr 2024 10:25:33 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Sean Christopherson <seanjc@...gle.com>
Cc: Xi Ruoyao <xry111@...111.site>, Dave Hansen
<dave.hansen@...ux.intel.com>, Michael Kelley <mhklinux@...look.com>,
Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
x86@...nel.org, linux-kernel@...r.kernel.org,
Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH v8 2/2] x86/mm: Don't disable PCID if the kernel is
running on a hypervisor
On 4/17/24 10:22, Pawan Gupta wrote:
>>> static const struct x86_cpu_id invlpg_miss_ids[] = {
>>> + /* Only bare-metal is affected. PCIDs in guests are OK. */
>>> + {
>>> + .vendor = X86_VENDOR_INTEL,
>>> + .family = 6,
>>> + .model = INTEL_FAM6_ANY,
>>> + .feature = X86_FEATURE_HYPERVISOR,
>> Isn't this inverted? x86_match_cpu() will return NULL if the CPU doesn't have
>> HYPERVISOR. We want it to return NULL if the CPU *does* have HYPERVISOR.
> I think the implementation is correct, x86_match_cpu() will not return
> NULL if the CPU doesn't have HYPERVISOR feature *and* matches one of the
> CPUs below. It will only return NULL if none of the entries match.
I think I gave a crappy suggestion here.
Let's just do the X86_FEATURE_HYPERVISOR explicitly in the code instead
of trying to cram it into the invlpg_miss_ids[] check. It's way easier
to understand with an explicit code check.
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