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Wed, 2 Sep 2026 21:15:37 +0000 Message-ID: Date: Wed, 2 Sep 2026 14:15:35 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/8] x86/fpu: Document reasoning of FX-only fallback To: Andrei Vagin , Thomas Gleixner , "Ingo Molnar" , Borislav Petkov CC: , , Dave Hansen , , Alexander Mikhalitsyn , "H. Peter Anvin" References: <20260817042048.1579415-1-avagin@google.com> <20260817042048.1579415-5-avagin@google.com> Content-Language: en-US From: "Chang S. 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To the kernel, this is one of handling options _once_ an error happens. This is for the better interaction with user space. > user-space state by resetting extended registers if the process was > using them but the frame metadata was malformed. > > Reviewed-by: Alexander Mikhalitsyn > Signed-off-by: Andrei Vagin > --- > arch/x86/kernel/fpu/signal.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c > index 6a14b528ac7f..85021c5ea649 100644 > --- a/arch/x86/kernel/fpu/signal.c > +++ b/arch/x86/kernel/fpu/signal.c > @@ -54,6 +54,14 @@ static inline bool check_xstate_in_sigframe(struct fxregs_state __user *buf_fx, > if (likely(magic2 == FP_XSTATE_MAGIC2)) > return true; > err_setfx: > + /* > + * The fallback to FX-only state is used to preserve backward > + * compatibility with user-space processes that are not aware of xsave > + * states. > + * > + * In all other cases, returning false (to trigger SIGSEGV) is > + * preferred to avoid silent user-space state corruption. > + */ > trace_x86_fpu_xstate_check_failed(x86_task_fpu(current)); > > /* Set the parameters for fx only state */ With all discussions in the past, yes. I'd vote for putting such comment on this path. With some massage in the changelog, Reviewed-by: Chang S. Bae Thanks, Chang