From: "Michael S. Tsirkin" <mst@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
andrey@xdel.ru
Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions
Date: Fri, 19 Jun 2015 18:45:00 +0200 [thread overview]
Message-ID: <20150619184220-mutt-send-email-mst@redhat.com> (raw)
In-Reply-To: <5583D85F.7090200@redhat.com>
On Fri, Jun 19, 2015 at 10:52:47AM +0200, Paolo Bonzini wrote:
>
>
> On 19/06/2015 10:05, Michael S. Tsirkin wrote:
> > > No, only destruction of the memory region frees it. address_space_map
> > > takes a reference to the memory region and address_space_unmap releases it.
> > >
> > > Paolo
> >
> > Confused. So can we call mmap(MAP_NORESERVE) in address_space_unmap
> > after we detect refcount is 0?
>
> No, because in the meanwhile another DIMM could have been hotplugged
> at the same place where the old one was. This is legal:
>
> user guest QEMU
> ----------------------------------------------------------------------------------------
> start I/O
> '---------------> address_space_map
> device_del
> '-------------------> receives SCI
> executes _EJ0
> '---------------> memory_region_del_subregion
> object_unparent
> device_add
> '-----------------------------------------> device_set_realized
> hotplug_handler_plug
> pc_machine_device_plug_cb
> pc_dimm_plug
> memory_region_add_subregion
>
> I/O finishes
> address_space_unmap
>
> Surprise removal similarly could be done in QEMU, but it will hold to
> some resources for as long as the device backends need them.
>
> Paolo
OK so what's the problem with checking for this condition,
after address_space_unmap detects that ref count is 0
and before calling mmap(MAP_NORESERVE)?
At that point we are off the data path so we can take locks.
--
MST
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
Please read the FAQ at http://www.tux.org/lkml/
WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
andrey@xdel.ru
Subject: Re: [PATCH 3/5] vhost: support upto 509 memory regions
Date: Fri, 19 Jun 2015 18:45:00 +0200 [thread overview]
Message-ID: <20150619184220-mutt-send-email-mst@redhat.com> (raw)
In-Reply-To: <5583D85F.7090200@redhat.com>
On Fri, Jun 19, 2015 at 10:52:47AM +0200, Paolo Bonzini wrote:
>
>
> On 19/06/2015 10:05, Michael S. Tsirkin wrote:
> > > No, only destruction of the memory region frees it. address_space_map
> > > takes a reference to the memory region and address_space_unmap releases it.
> > >
> > > Paolo
> >
> > Confused. So can we call mmap(MAP_NORESERVE) in address_space_unmap
> > after we detect refcount is 0?
>
> No, because in the meanwhile another DIMM could have been hotplugged
> at the same place where the old one was. This is legal:
>
> user guest QEMU
> ----------------------------------------------------------------------------------------
> start I/O
> '---------------> address_space_map
> device_del
> '-------------------> receives SCI
> executes _EJ0
> '---------------> memory_region_del_subregion
> object_unparent
> device_add
> '-----------------------------------------> device_set_realized
> hotplug_handler_plug
> pc_machine_device_plug_cb
> pc_dimm_plug
> memory_region_add_subregion
>
> I/O finishes
> address_space_unmap
>
> Surprise removal similarly could be done in QEMU, but it will hold to
> some resources for as long as the device backends need them.
>
> Paolo
OK so what's the problem with checking for this condition,
after address_space_unmap detects that ref count is 0
and before calling mmap(MAP_NORESERVE)?
At that point we are off the data path so we can take locks.
--
MST
next prev parent reply other threads:[~2015-06-19 16:45 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-16 16:33 [PATCH 0/5] vhost: support upto 509 memory regions Igor Mammedov
2015-06-16 16:33 ` [PATCH 1/5] vhost: use binary search instead of linear in find_region() Igor Mammedov
2015-06-16 21:07 ` Michael S. Tsirkin
2015-06-16 21:13 ` Igor Mammedov
2015-06-16 16:33 ` [PATCH 2/5] vhost: extend memory regions allocation to vmalloc Igor Mammedov
2015-06-16 16:33 ` [PATCH 3/5] vhost: support upto 509 memory regions Igor Mammedov
2015-06-16 21:14 ` Michael S. Tsirkin
2015-06-16 22:00 ` Igor Mammedov
2015-06-17 6:34 ` Michael S. Tsirkin
2015-06-17 7:28 ` Igor Mammedov
2015-06-17 7:39 ` Michael S. Tsirkin
2015-06-17 8:54 ` Igor Mammedov
2015-06-17 10:11 ` Michael S. Tsirkin
2015-06-17 10:37 ` Igor Mammedov
2015-06-17 10:46 ` Michael S. Tsirkin
2015-06-17 11:48 ` Igor Mammedov
2015-06-17 11:51 ` Michael S. Tsirkin
2015-06-17 12:23 ` Igor Mammedov
2015-06-17 13:13 ` Michael S. Tsirkin
2015-06-17 13:20 ` Paolo Bonzini
2015-06-17 14:32 ` Michael S. Tsirkin
2015-06-17 15:12 ` Igor Mammedov
2015-06-17 15:38 ` Michael S. Tsirkin
2015-06-17 16:09 ` Igor Mammedov
2015-06-17 16:30 ` Michael S. Tsirkin
2015-06-17 16:31 ` Paolo Bonzini
2015-06-17 16:34 ` Michael S. Tsirkin
2015-06-17 16:38 ` Paolo Bonzini
2015-06-17 16:41 ` Michael S. Tsirkin
2015-06-17 16:47 ` Paolo Bonzini
2015-06-17 17:32 ` Igor Mammedov
2015-06-17 19:11 ` Michael S. Tsirkin
2015-06-17 17:30 ` Igor Mammedov
2015-06-18 9:12 ` Igor Mammedov
2015-06-18 9:50 ` Michael S. Tsirkin
2015-06-18 10:03 ` Paolo Bonzini
2015-06-18 11:39 ` Igor Mammedov
2015-06-18 11:41 ` Michael S. Tsirkin
2015-06-18 11:50 ` Paolo Bonzini
2015-06-18 13:19 ` Michael S. Tsirkin
2015-06-18 13:46 ` Paolo Bonzini
2015-06-18 14:47 ` Michael S. Tsirkin
2015-06-18 15:54 ` Igor Mammedov
2015-06-18 16:02 ` Paolo Bonzini
2015-06-19 7:56 ` Michael S. Tsirkin
2015-06-19 7:57 ` Paolo Bonzini
2015-06-19 8:05 ` Michael S. Tsirkin
2015-06-19 8:52 ` Paolo Bonzini
2015-06-19 10:14 ` Michael S. Tsirkin
2015-06-19 10:44 ` Paolo Bonzini
2015-06-19 13:34 ` Michael S. Tsirkin
2015-06-19 13:34 ` Michael S. Tsirkin
2015-06-19 15:19 ` Paolo Bonzini
2015-06-19 15:19 ` Paolo Bonzini
2015-06-19 16:20 ` Michael S. Tsirkin
2015-06-19 16:20 ` Michael S. Tsirkin
2015-06-19 16:26 ` Paolo Bonzini
2015-06-19 16:26 ` Paolo Bonzini
2015-06-19 16:33 ` Michael S. Tsirkin
2015-06-19 16:33 ` Michael S. Tsirkin
2015-06-19 16:44 ` Paolo Bonzini
2015-06-19 16:44 ` Paolo Bonzini
2015-06-22 7:10 ` Igor Mammedov
2015-06-22 7:10 ` Igor Mammedov
2015-06-22 9:45 ` Paolo Bonzini
2015-06-22 9:45 ` Paolo Bonzini
2015-06-19 16:45 ` Michael S. Tsirkin [this message]
2015-06-19 16:45 ` Michael S. Tsirkin
2015-06-19 16:50 ` Paolo Bonzini
2015-06-19 16:50 ` Paolo Bonzini
2015-06-18 12:02 ` Igor Mammedov
2015-06-17 8:53 ` Paolo Bonzini
2015-06-16 16:33 ` [PATCH 4/5] vhost: add per VQ memory region caching Igor Mammedov
2015-06-16 16:33 ` [PATCH 5/5] vhost: translate_desc: optimization for desc.len < region size Igor Mammedov
2015-06-16 21:11 ` Michael S. Tsirkin
2015-06-16 21:16 ` [PATCH 0/5] vhost: support upto 509 memory regions Michael S. Tsirkin
2015-06-16 22:19 ` Igor Mammedov
2015-06-17 6:31 ` Michael S. Tsirkin
2015-06-17 7:33 ` Igor Mammedov
2015-06-17 7:40 ` Michael S. Tsirkin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150619184220-mutt-send-email-mst@redhat.com \
--to=mst@redhat.com \
--cc=andrey@xdel.ru \
--cc=imammedo@redhat.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.