linux-kernel - Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)

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Message-ID: <CA+55aFxJF88EJ=WhPq08j4+REBgpvVHVwbg5BR05DD+exRyp8A@mail.gmail.com>
Date:	Tue, 23 Aug 2011 09:29:29 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Borislav Petkov <bp@...64.org>
Cc:	Andrew Lutomirski <luto@....edu>,
	Al Viro <viro@...iv.linux.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	"user-mode-linux-devel@...ts.sourceforge.net" 
	<user-mode-linux-devel@...ts.sourceforge.net>,
	Richard Weinberger <richard@....at>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>
Subject: Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re:
 [RFC] weird crap with vdso on uml/i386)

On Tue, Aug 23, 2011 at 9:22 AM, Borislav Petkov <bp@...64.org> wrote:
>
> I don't think that removing SYSCALL from 32-bit code just so that UML
> trapped syscalls work is something we'd like since SYSCALL is much
> cheaper than INT $0x80:

Oh yes.

System call performance is *important*. And x86 is *important*.

UML? In comparison, not that important.

So quite frankly, if this is purely an UML issue (and unless we're
missing something else, that's what it looks like, despite all the
confusion we've had so far), then if we have a choice between "remove
syscall instruction" and "remove UML", then ...

                           Linus
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