linux-kernel - Re: [PATCH v6 02/25] x86/fpu/xstate: Fix guest fpstate allocation size calculation

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Message-ID: <d05a91f12cbce9827911c23afcfa5fdaf2acb5cf.camel@intel.com>
Date:   Thu, 14 Sep 2023 22:45:50 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Yang, Weijiang" <weijiang.yang@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "peterz@...radead.org" <peterz@...radead.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "john.allen@....com" <john.allen@....com>
Subject: Re: [PATCH v6 02/25] x86/fpu/xstate: Fix guest fpstate allocation
 size calculation

On Thu, 2023-09-14 at 02:33 -0400, Yang Weijiang wrote:
> Fix guest xsave area allocation size from fpu_user_cfg.default_size
> to
> fpu_kernel_cfg.default_size so that the xsave area size is consistent
> with fpstate->size set in __fpstate_reset().
> 
> With the fix, guest fpstate size is sufficient for KVM supported
> guest
> xfeatures.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>

There is no fix (Fixes: ...) here, right? I think this change is needed
to make sure KVM guests can support supervisor features. But KVM CET
support (to follow in future patches) will be the first one, right?

The side effect will be that KVM guest FPUs now get guaranteed room for
PASID as well as CET. I think I remember you mentioned that due to
alignment requirements, there shouldn't usually be any size change
though? It might be nice to add that in the log, if I'm remembering
correctly.