From: Peter Zijlstra <peterz@infradead.org>
To: "Jürgen Groß" <jgross@suse.com>
Cc: xen-devel@lists.xenproject.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH] x86/alternative: don't call text_poke() in lazy TLB mode
Date: Mon, 12 Oct 2020 12:45:08 +0200 [thread overview]
Message-ID: <20201012104508.GS2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <fc202e90-00ff-a635-f298-c3ca293e9182@suse.com>
On Mon, Oct 12, 2020 at 12:26:06PM +0200, Jürgen Groß wrote:
> > > @@ -807,6 +807,15 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
> > > temp_mm_state_t temp_state;
> > > lockdep_assert_irqs_disabled();
> > > +
> > > + /*
> > > + * Make sure not to be in TLB lazy mode, as otherwise we'll end up
> > > + * with a stale address space WITHOUT being in lazy mode after
> > > + * restoring the previous mm.
> > > + */
> > > + if (this_cpu_read(cpu_tlbstate.is_lazy))
> > > + leave_mm(smp_processor_id());
> > > +
> > > temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm);
> > > switch_mm_irqs_off(NULL, mm, current);
> >
> > Would it make sense to write it like:
> >
> > this_state.mm = this_cpu_read(cpu_tlbstate.is_lazy) ?
> > &init_mm : this_cpu_read(cpu_tlbstate.loaded_mm);
> >
> > Possibly with that wrapped in a conveniently named helper function.
>
> Fine with me, but I don't think it matters that much.
>
> For each batch of text_poke() it will be hit only once, and I'm not sure
> it is really a good idea to use the knowledge that leave_mm() is just a
> switch to init_mm here.
Yeah, I'm not sure either. But it's something I came up with when
looking at all this.
Andy, what's your preference?
next prev parent reply other threads:[~2020-10-12 10:45 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-09 14:42 [PATCH] x86/alternative: don't call text_poke() in lazy TLB mode Juergen Gross
2020-10-12 10:13 ` Peter Zijlstra
2020-10-12 10:26 ` Jürgen Groß
2020-10-12 10:45 ` Peter Zijlstra [this message]
2020-10-22 9:24 ` Jürgen Groß
2020-10-22 10:45 ` Peter Zijlstra
2020-10-22 10:48 ` Jürgen Groß
2020-10-22 10:49 ` [tip: x86/urgent] x86/alternative: Don't " tip-bot2 for Juergen Gross
2020-10-22 17:50 ` Andy Lutomirski
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