linux-kernel - Re: [PATCH 4/8] x86/vm86: Use the normal pt

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Message-ID: <CA+55aFzM4Y4Bfu1vwFF_eKj5uRFVpEgQZLby4U-zSBBPBOTVuQ@mail.gmail.com>
Date:	Wed, 29 Jul 2015 10:47:17 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Brian Gerst <brgerst@...il.com>
Cc:	Andy Lutomirski <luto@...capital.net>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [PATCH 4/8] x86/vm86: Use the normal pt_regs area for vm86

On Wed, Jul 29, 2015 at 10:36 AM, Brian Gerst <brgerst@...il.com> wrote:
>
> I think I remember now what the issue was.  Since entering vm86 mode
> uses force_iret(), the work_pending code path was being taken.  I had
> to move the call to save_v86_state out of here to handle_signal(),
> otherwise it would just restore the 32-bit regs and exit the syscall
> without ever entering vm86 mode.  But that meant that the test for
> kernel CS was seeing the vm86 regs instead of 32-bit regs, and was
> failing because it didn't account for the VM bit (if the real-mode CS
> looked like RPL 0).  A fault would get stuck in a loop because it
> couldn't exit to the signal handling code.

Hmm. I think we'd want a big comment about that code then, and how it
is only used for user-space (including vm86 mode).

                Linus
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