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Date: Tue, 17 Mar 2015 14:51:28 +0100 From: Denys Vlasenko <dvlasenk@...hat.com> To: Ingo Molnar <mingo@...nel.org> CC: Denys Vlasenko <dvlasenk@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Steven Rostedt <rostedt@...dmis.org>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...capital.net>, Oleg Nesterov <oleg@...hat.com>, Frederic Weisbecker <fweisbec@...il.com>, Alexei Starovoitov <ast@...mgrid.com>, Will Drewry <wad@...omium.org>, Kees Cook <keescook@...omium.org>, x86@...nel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/2] x86/asm/entry/64: Enable interrupts *after* we fetch PER_CPU_VAR(old_rsp) On 03/17/2015 02:42 PM, Denys Vlasenko wrote: > Without this change, it is still not possible to get rid of > PER_CPU_VAR(old_rsp) usage in switch_to: if preemption happens > while we did not fetch PER_CPU_VAR(old_rsp) and stored it in pt_regs->sp, > PER_CPU_VAR(old_rsp) gets corrupted by other task's user sp. > > Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com> > CC: Linus Torvalds <torvalds@...ux-foundation.org> > CC: Steven Rostedt <rostedt@...dmis.org> > CC: Ingo Molnar <mingo@...nel.org> > CC: Borislav Petkov <bp@...en8.de> > CC: "H. Peter Anvin" <hpa@...or.com> > CC: Andy Lutomirski <luto@...capital.net> > CC: Oleg Nesterov <oleg@...hat.com> > CC: Frederic Weisbecker <fweisbec@...il.com> > CC: Alexei Starovoitov <ast@...mgrid.com> > CC: Will Drewry <wad@...omium.org> > CC: Kees Cook <keescook@...omium.org> > CC: x86@...nel.org > CC: linux-kernel@...r.kernel.org > --- > > Run-tested, including with PARAVIRT on. Well. The testing with PARAVIRT did work, however, I don't know why. > movq_cfi rax,ORIG_RAX > + /* > + * No need to follow this irqs off/on section - it's straight > + * and short: > + */ > + ENABLE_INTERRUPTS(CLBR_RAX) Here I wrongly assumed that now I can clobber rax, since it is saved in pt_regs->orig_ax now. Wrong. Code below still wants to use rax register directly. Looks like I was "lucky" and paravirt call happen to not change rax. I'll send a v2 patch without this ill-advised attempt of optimization. Sorry. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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