linux-kernel - Re: [PATCH 05/22] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to

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Date:   Tue, 22 Jan 2019 17:15:51 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...riel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 05/22] x86/fpu: Remove fpu->initialized usage in
 copy_fpstate_to_sigframe()

On 01/22, Borislav Petkov wrote:
>
> On Mon, Jan 21, 2019 at 12:21:17PM +0100, Oleg Nesterov wrote:
> > And in any case I do not understand the idea to use the second
> > in-kernel struct fpu. A signal handler can be interrupted by another
> > signal, this will need to save/restore the FPU state again.
>
> Well, we were just speculating whether doing that would simplify the
> code around get_sigframe() et al. But if that is an ABI, then we can't
> really touch it.
>
> Btw, where is that whole ABI deal about saving FPU regs on the user
> signal stack documented?

I don't know... tried to google, found nothing.

the comment in /usr/include/sys/ucontext.h mentions SysV/i386 ABI + historical
reasons, this didn't help.

Oleg.