linux-kernel - Re: [PATCH v3 04/10] x86/fpu/xstate: Correct guest fpstate size calculation

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Message-ID: <4e18ddd0-a122-449b-bbbd-aeed3475a324@intel.com>
Date: Fri, 7 Mar 2025 09:53:40 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Chao Gao <chao.gao@...el.com>, tglx@...utronix.de, x86@...nel.org,
 seanjc@...gle.com, pbonzini@...hat.com, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org
Cc: peterz@...radead.org, rick.p.edgecombe@...el.com,
 weijiang.yang@...el.com, john.allen@....com, bp@...en8.de
Subject: Re: [PATCH v3 04/10] x86/fpu/xstate: Correct guest fpstate size
 calculation

On 3/7/25 08:41, Chao Gao wrote:
> Note that this issue does not cause any functional problems because the
> guest fpstate is allocated using vmalloc(), which aligns the size to a
> full page, providing enough space for all existing supervisor components.
> On Emerald Rapids CPUs, the guest fpstate after this correction is ~2880
> bytes.

How about we move up the fpstate pointers at allocation time so they
just scrape the end of the vmalloc buffer? Basically, move the
page-alignment padding to the beginning of the first page instead of the
end of the last page.