From: Andrea Arcangeli <aarcange@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: Jerome Glisse <jglisse@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
peterx@redhat.com, linux-mm@kvack.org, Jan Kara <jack@suse.cz>
Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address
Date: Fri, 8 Mar 2019 14:11:08 -0500 [thread overview]
Message-ID: <20190308191108.GA26923@redhat.com> (raw)
In-Reply-To: <671c4a98-4699-836e-79fc-0ce650c7f701@redhat.com>
On Fri, Mar 08, 2019 at 05:13:26PM +0800, Jason Wang wrote:
> Actually not wrapping around, the pages for used ring was marked as
> dirty after a round of virtqueue processing when we're sure vhost wrote
> something there.
Thanks for the clarification. So we need to convert it to
set_page_dirty and move it to the mmu notifier invalidate but in those
cases where gup_fast was called with write=1 (1 out of 3).
If using ->invalidate_range the page pin also must be removed
immediately after get_user_pages returns (not ok to hold the pin in
vmap until ->invalidate_range is called) to avoid false positive gup
pin checks in things like KSM, or the pin must be released in
invalidate_range_start (which is called before the pin checks).
Here's why:
/*
* Check that no O_DIRECT or similar I/O is in progress on the
* page
*/
if (page_mapcount(page) + 1 + swapped != page_count(page)) {
set_pte_at(mm, pvmw.address, pvmw.pte, entry);
goto out_unlock;
}
[..]
set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
^^^^^^^ too late release the pin here, the
above already failed
->invalidate_range cannot be used with mutex anyway so you need to go
back with invalidate_range_start/end anyway, just the pin must be
released in _start at the latest in such case.
My prefer is generally to call gup_fast() followed by immediate
put_page() because I always want to drop FOLL_GET from gup_fast as a
whole to avoid 2 useless atomic ops per gup_fast.
I'll write more about vmap in answer to the other email.
Thanks,
Andrea
next prev parent reply other threads:[~2019-03-08 19:11 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-06 7:18 [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 1/5] vhost: generalize adding used elem Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 2/5] vhost: fine grain userspace memory accessors Jason Wang
2019-03-06 10:45 ` Christophe de Dinechin
2019-03-07 2:38 ` Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 3/5] vhost: rename vq_iotlb_prefetch() to vq_meta_prefetch() Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 4/5] vhost: introduce helpers to get the size of metadata area Jason Wang
2019-03-06 10:56 ` Christophe de Dinechin
2019-03-07 2:40 ` Jason Wang
2019-03-06 18:43 ` Souptick Joarder
2019-03-07 2:42 ` Jason Wang
2019-03-06 7:18 ` [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address Jason Wang
2019-03-06 16:31 ` Michael S. Tsirkin
2019-03-07 2:45 ` Jason Wang
2019-03-07 15:34 ` Michael S. Tsirkin
2019-03-07 19:09 ` Jerome Glisse
2019-03-07 19:38 ` Andrea Arcangeli
2019-03-07 20:17 ` Jerome Glisse
2019-03-07 21:27 ` Andrea Arcangeli
2019-03-08 9:13 ` Jason Wang
2019-03-08 19:11 ` Andrea Arcangeli [this message]
2019-03-11 7:21 ` Jason Wang
2019-03-11 14:45 ` Jan Kara
2019-03-08 8:31 ` Jason Wang
2019-03-07 15:47 ` Michael S. Tsirkin
2019-03-07 17:56 ` Michael S. Tsirkin
2019-03-07 19:16 ` Andrea Arcangeli
2019-03-08 8:50 ` Jason Wang
2019-03-08 14:58 ` Jerome Glisse
2019-03-11 7:18 ` Jason Wang
2019-03-08 19:48 ` Andrea Arcangeli
2019-03-08 20:06 ` Jerome Glisse
2019-03-11 7:40 ` Jason Wang
2019-03-11 12:48 ` Michael S. Tsirkin
2019-03-11 13:43 ` Andrea Arcangeli
2019-03-12 2:56 ` Jason Wang
2019-03-12 3:51 ` Michael S. Tsirkin
2019-03-12 2:52 ` Jason Wang
2019-03-12 3:50 ` Michael S. Tsirkin
2019-03-12 7:15 ` Jason Wang
2019-03-07 19:17 ` Jerome Glisse
2019-03-08 2:21 ` Michael S. Tsirkin
2019-03-08 2:55 ` Jerome Glisse
2019-03-08 3:16 ` Michael S. Tsirkin
2019-03-08 3:40 ` Jerome Glisse
2019-03-08 3:43 ` Michael S. Tsirkin
2019-03-08 3:45 ` Jerome Glisse
2019-03-08 9:15 ` Jason Wang
2019-03-08 8:58 ` Jason Wang
2019-03-08 12:56 ` Michael S. Tsirkin
2019-03-08 15:02 ` Jerome Glisse
2019-03-08 19:13 ` Andrea Arcangeli
2019-03-08 14:12 ` [RFC PATCH V2 0/5] vhost: accelerate metadata access through vmap() Christoph Hellwig
2019-03-11 7:13 ` Jason Wang
2019-03-11 13:59 ` Michael S. Tsirkin
2019-03-11 18:14 ` David Miller
2019-03-12 2:59 ` Jason Wang
2019-03-12 3:52 ` Michael S. Tsirkin
2019-03-12 7:17 ` Jason Wang
2019-03-12 11:54 ` Michael S. Tsirkin
2019-03-12 15:46 ` James Bottomley
2019-03-12 20:04 ` Andrea Arcangeli
2019-03-12 20:53 ` James Bottomley
2019-03-12 21:11 ` Andrea Arcangeli
2019-03-12 21:19 ` James Bottomley
2019-03-12 21:53 ` Andrea Arcangeli
2019-03-12 22:02 ` James Bottomley
2019-03-12 22:50 ` Andrea Arcangeli
2019-03-12 22:57 ` James Bottomley
2019-03-13 16:05 ` Christoph Hellwig
2019-03-13 16:37 ` James Bottomley
2019-03-14 10:42 ` Michael S. Tsirkin
2019-03-14 13:49 ` Jason Wang
2019-03-14 19:33 ` Andrea Arcangeli
2019-03-15 4:39 ` Jason Wang
2019-03-12 5:14 ` James Bottomley
2019-03-12 7:51 ` Jason Wang
2019-03-12 7:53 ` Jason Wang
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