linux-kernel - Re: [PATCH 10/24] x86/mm/kaiser: Map the entry stack variables

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Message-ID: <20171127210016.jj4sqaymlkvxrmej@hirez.programming.kicks-ass.net>
Date:   Mon, 27 Nov 2017 22:00:16 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 10/24] x86/mm/kaiser: Map the entry stack variables

On Mon, Nov 27, 2017 at 06:32:11PM +0100, Thomas Gleixner wrote:
> On Mon, 27 Nov 2017, Peter Zijlstra wrote:
> 
> > On Mon, Nov 27, 2017 at 11:49:09AM +0100, Ingo Molnar wrote:
> > > diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> > > index 157f81816915..631e229ab428 100644
> > > --- a/arch/x86/kernel/process_64.c
> > > +++ b/arch/x86/kernel/process_64.c
> > > @@ -59,7 +59,7 @@
> > >  #include <asm/unistd_32_ia32.h>
> > >  #endif
> > >  
> > > -__visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
> > > +__visible DEFINE_PER_CPU_USER_MAPPED(unsigned long, rsp_scratch);
> > >  
> > >  /* Prints also some state that isn't saved in the pt_regs */
> > >  void __show_regs(struct pt_regs *regs, int all)
> > 
> > Do we still need this one? It appears to me we'll never actually execute
> > that part of entry_SYSCALL_64 anymore, due to
> > entry_SYSCALL_64_trampoline.
> 
> Unless we use entry_SYSCALL_64 when kaiser is disabled at boottime

Right for which you need that patchlet I send earlier today. The patches
as they are will never ever reach that code.