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Message-ID: <c8369a44-f4e0-4132-b470-cca7a044bb02@redhat.com> Date: Tue, 14 May 2019 11:42:11 +0800 From: Jason Wang <jasowang@...hat.com> To: David Miller <davem@...emloft.net> Cc: mst@...hat.com, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, hch@...radead.org, James.Bottomley@...senPartnership.com, aarcange@...hat.com, tglx@...utronix.de, mingo@...hat.com, peterz@...radead.org, dvhart@...radead.org Subject: Re: [PATCH net] vhost: don't use kmap() to log dirty pages On 2019/5/14 上午12:42, David Miller wrote: > From: Jason Wang <jasowang@...hat.com> > Date: Mon, 13 May 2019 01:27:45 -0400 > >> Vhost log dirty pages directly to a userspace bitmap through GUP and >> kmap_atomic() since kernel doesn't have a set_bit_to_user() >> helper. This will cause issues for the arch that has virtually tagged >> caches. The way to fix is to keep using userspace virtual >> address. Fortunately, futex has arch_futex_atomic_op_inuser() which >> could be used for setting a bit to user. >> >> Note there're several cases that futex helper can fail e.g a page >> fault or the arch that doesn't have the support. For those cases, a >> simplified get_user()/put_user() pair protected by a global mutex is >> provided as a fallback. The fallback may lead false positive that >> userspace may see more dirty pages. >> >> Cc: Christoph Hellwig <hch@...radead.org> >> Cc: James Bottomley <James.Bottomley@...senPartnership.com> >> Cc: Andrea Arcangeli <aarcange@...hat.com> >> Cc: Thomas Gleixner <tglx@...utronix.de> >> Cc: Ingo Molnar <mingo@...hat.com> >> Cc: Peter Zijlstra <peterz@...radead.org> >> Cc: Darren Hart <dvhart@...radead.org> >> Fixes: 3a4d5c94e9593 ("vhost_net: a kernel-level virtio server") >> Signed-off-by: Jason Wang <jasowang@...hat.com> > I want to see a review from Michael for this change before applying. No problem, since kbuild spotted an issue. Let me post V2. Thanks
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