linux-kernel - Re: AMD DC graphics display code enables -mhard-float, -msse, -msse2 without any visible FPU state protection

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Message-Id: <20200408004111.3dd597f2a7c6172b4c71a9ba@kernel.org>
Date:   Wed, 8 Apr 2020 00:41:11 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Christian König <christian.koenig@....com>,
        Jann Horn <jannh@...gle.com>,
        Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>, amd-gfx@...ts.freedesktop.org,
        Alex Deucher <alexander.deucher@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: AMD DC graphics display code enables -mhard-float, -msse,
 -msse2 without any visible FPU state protection

On Tue, 7 Apr 2020 13:15:35 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Apr 07, 2020 at 06:50:08PM +0900, Masami Hiramatsu wrote:
> > On Mon, 6 Apr 2020 12:21:07 +0200
> > Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > > arch/x86/mm/extable.o: warning: objtool: ex_handler_fprestore()+0x8b: fpu_safe hint not an FPU instruction
> > > 008b  36b:      48 0f ae 0d 00 00 00    fxrstor64 0x0(%rip)        # 373 <ex_handler_fprestore+0x93>
> > > 
> > > arch/x86/kvm/x86.o: warning: objtool: kvm_load_guest_fpu.isra.0()+0x1fa: fpu_safe hint not an FPU instruction
> > > 01fa    1d2fa:  48 0f ae 4b 40          fxrstor64 0x40(%rbx)
> > 
> > Ah, fxstor will not chang the FPU/MMX/SSE regs but just store it on memory.
> > OK, I'll remove it from the list.
> 
> Yeah, I don't much care if its in or out, but the way I was reading that
> patch it _should_ be in, but then it doesn't seem to recognise it.

Oops, I misread. OK. I fixed the issue.

> 
> > > Also, all the VMX bits seems to qualify as FPU (I can't remember seeing
> > > that previously):
> > 
> > Oops, let me check it.
> 
> I just send you another patch that could do with insn_is_vmx()
> (sorry!!!)

Hmm, it is hard to find out the vmx insns. Maybe we need to clarify it by
opcode pattern. (like "VM.*")

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>