From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH 05/22] x86/fpu: Remove fpu->initialized usage in
 copy_fpstate_to_sigframe()
Date: Tue, 22 Jan 2019 17:15:51 +0100
Message-ID: <20190122161551.GB9745@redhat.com>
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Cc: Dave Hansen <dave.hansen@intel.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        x86@kernel.org, Andy Lutomirski <luto@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        kvm@vger.kernel.org, "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Rik van Riel <riel@surriel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
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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.