linux-kernel - Re: [PATCH 2/2] s390/fpu: Fix kmsan in fpu

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Message-ID: <20251107104926.17578C07-hca@linux.ibm.com>
Date: Fri, 7 Nov 2025 11:49:26 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Alexander Potapenko <glider@...gle.com>
Cc: Aleksei Nikiforov <aleksei.nikiforov@...ux.ibm.com>,
        Marco Elver <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
        Juergen Christ <jchrist@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: Re: [PATCH 2/2] s390/fpu: Fix kmsan in fpu_vstl function

On Fri, Nov 07, 2025 at 11:26:50AM +0100, Alexander Potapenko wrote:
> On Thu, Nov 6, 2025 at 5:09 PM Aleksei Nikiforov
> <aleksei.nikiforov@...ux.ibm.com> wrote:
> > @@ -409,6 +410,7 @@ static __always_inline void fpu_vstl(u8 v1, u32 index, const void *vxr)
> >                 : [vxr] "=R" (*(u8 *)vxr)
> >                 : [index] "d" (index), [v1] "I" (v1)
> >                 : "memory", "1");
> > +       instrument_write_after(vxr, size);
> >  }
> 
> Wouldn't it be easier to just call kmsan_unpoison_memory() here directly?

I guess that's your call. Looks like we have already a couple of
kmsan_unpoison_memory() behind inline assemblies.

So I guess we should either continue using kmsan_unpoison_memory()
directly, or convert all of them to such a new helper. Both works of
course. What do you prefer?