From: "Emilio G. Cota" <cota@braap.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Alex Bennée" <alex.bennee@linaro.org>,
qemu-devel@nongnu.org, "Richard Henderson" <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH 2/3] cputlb: serialize tlb updates with env->tlb_lock
Date: Wed, 3 Oct 2018 14:07:31 -0400 [thread overview]
Message-ID: <20181003180731.GA26376@flamenco> (raw)
In-Reply-To: <d966f99b-4a37-4a00-0267-50adabb3675f@redhat.com>
On Wed, Oct 03, 2018 at 19:05:51 +0200, Paolo Bonzini wrote:
> On 03/10/2018 19:02, Emilio G. Cota wrote:
> >> For reads I agree, but you may actually get a torn read if the writer
> >> doesn't use atomic_set.
> >
> > But you cannot get a torn read if all reads that don't hold the lock
> > are coming from the same thread that performed the write.
>
> Ah, so you are relying on copy_tlb_helper(_locked) being invoked only
> from the vCPU thread (as opposed to someone else doing tlb_flush)?
Yes. tlb_flush_nocheck is always run by the owner thread--tlb_flush
checks for this, and if !qemu_cpu_is_self(cpu) then it schedules
async work on the owner thread.
> Maybe it's worth adding a comment if that's what I missed.
I'll send a v2 with an updated comment and a debug-only assert
in the copy helper.
Thanks,
E.
next prev parent reply other threads:[~2018-10-03 18:07 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-02 21:29 [Qemu-devel] [PATCH 0/3] per-TLB lock Emilio G. Cota
2018-10-02 21:29 ` [Qemu-devel] [PATCH 1/3] exec: introduce tlb_init Emilio G. Cota
2018-10-02 21:29 ` [Qemu-devel] [PATCH 2/3] cputlb: serialize tlb updates with env->tlb_lock Emilio G. Cota
2018-10-03 9:19 ` Alex Bennée
2018-10-03 10:02 ` Paolo Bonzini
2018-10-03 15:48 ` Emilio G. Cota
2018-10-03 15:52 ` Paolo Bonzini
2018-10-03 17:02 ` Emilio G. Cota
2018-10-03 17:05 ` Paolo Bonzini
2018-10-03 18:07 ` Emilio G. Cota [this message]
2018-10-02 21:29 ` [Qemu-devel] [PATCH 3/3] cputlb: read CPUTLBEntry.addr_write atomically Emilio G. Cota
2018-10-03 7:56 ` [Qemu-devel] [PATCH 0/3] per-TLB lock Paolo Bonzini
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