linux-kernel - Re: [PATCH 3/3] x86/mm, tracing: Fix CR2 corruption

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Message-ID: <20190703220522.GK3402@hirez.programming.kicks-ass.net>
Date:   Thu, 4 Jul 2019 00:05:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        He Zhe <zhe.he@...driver.com>,
        Joel Fernandes <joel@...lfernandes.org>, devel@...ukata.com
Subject: Re: [PATCH 3/3] x86/mm, tracing: Fix CR2 corruption

On Wed, Jul 03, 2019 at 04:47:01PM -0400, Steven Rostedt wrote:
> On Wed, 3 Jul 2019 13:27:09 -0700
> Andy Lutomirski <luto@...nel.org> wrote:
> 
> 
> > > @@ -1180,10 +1189,10 @@ idtentry xenint3                do_int3                 has_error_co
> > >  #endif
> > >
> > >  idtentry general_protection    do_general_protection   has_error_code=1
> > > -idtentry page_fault            do_page_fault           has_error_code=1
> > > +idtentry page_fault            do_page_fault           has_error_code=1        read_cr2=1
> > >
> > >  #ifdef CONFIG_KVM_GUEST
> > > -idtentry async_page_fault      do_async_page_fault     has_error_code=1
> > > +idtentry async_page_fault      do_async_page_fault     has_error_code=1        read_cr2=1
> > >  #endif
> > >
> > >  #ifdef CONFIG_X86_MCE
> > > @@ -1338,18 +1347,9 @@ ENTRY(error_entry)
> > >         movq    %rax, %rsp                      /* switch stack */
> > >         ENCODE_FRAME_POINTER
> > >         pushq   %r12
> > > -
> > > -       /*
> > > -        * We need to tell lockdep that IRQs are off.  We can't do this until
> > > -        * we fix gsbase, and we should do it before enter_from_user_mode
> > > -        * (which can take locks).
> > > -        */
> > > -       TRACE_IRQS_OFF  
> > 
> > This hunk looks wrong.  Am I missing some other place that handles the
> > case where we enter from kernel mode and IRQs were on?
> 
> Yeah, looks like we might be missing a TRACE_IRQS_OFF from the
> from_usermode_stack_switch path.

Oh bugger, there's a second error_entry call.