From: Peter Xu <peterx@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
qemu-devel@nongnu.org, Cornelia Huck <cohuck@redhat.com>,
kvm@vger.kernel.org, david@redhat.com
Subject: Re: [Qemu-devel] [PATCH v3 0/4] Balloon inhibit enhancements, vfio restriction
Date: Wed, 8 Aug 2018 11:45:43 +0800 [thread overview]
Message-ID: <20180808034543.GC24415@xz-mi> (raw)
In-Reply-To: <20180808004929-mutt-send-email-mst@kernel.org>
On Wed, Aug 08, 2018 at 12:58:32AM +0300, Michael S. Tsirkin wrote:
> At least with VTD, it seems entirely possible to change e.g. a PMD
> atomically to point to a different set of PTEs, then flush.
> That will allow removing memory at high granularity for
> an arbitrary device without mdev or PASID dependency.
My understanding is that the guest driver should prohibit this kind of
operation (say, modifying PMD). Actually I don't see how it can
happen in Linux if the kernel drivers always call the IOMMU API since
there are only map/unmap APIs rather than this atomic-modify API.
The thing is that IMHO it's the guest driver's responsibility to make
sure the pages will never be used by the device before it removes the
entry (including modifying the PMD since that actually removes all the
entries on the old PMD). If not, I would see it a guest kernel bug
instead of the bug in the emulation code.
Thanks,
--
Peter Xu
next prev parent reply other threads:[~2018-08-08 3:46 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-07 19:31 [Qemu-devel] [PATCH v3 0/4] Balloon inhibit enhancements, vfio restriction Alex Williamson
2018-08-07 19:31 ` [Qemu-devel] [PATCH v3 1/4] balloon: Allow multiple inhibit users Alex Williamson
2018-08-07 19:44 ` Michael S. Tsirkin
2018-08-07 20:08 ` Alex Williamson
2018-08-08 0:07 ` Michael S. Tsirkin
2018-08-07 19:31 ` [Qemu-devel] [PATCH v3 2/4] kvm: Use inhibit to prevent ballooning without synchronous mmu Alex Williamson
2018-08-16 18:15 ` Alex Williamson
2018-08-17 7:46 ` Paolo Bonzini
2018-08-07 19:31 ` [Qemu-devel] [PATCH v3 3/4] vfio: Inhibit ballooning based on group attachment to a container Alex Williamson
2018-08-08 3:38 ` Peter Xu
2018-08-07 19:31 ` [Qemu-devel] [PATCH v3 4/4] vfio/ccw/pci: Allow devices to opt-in for ballooning Alex Williamson
2018-08-07 19:44 ` [Qemu-devel] [PATCH v3 0/4] Balloon inhibit enhancements, vfio restriction Michael S. Tsirkin
2018-08-07 19:53 ` Alex Williamson
2018-08-07 21:58 ` Michael S. Tsirkin
2018-08-07 22:40 ` Alex Williamson
2018-08-08 0:02 ` Michael S. Tsirkin
2018-08-08 3:45 ` Peter Xu [this message]
2018-08-08 22:23 ` Alex Williamson
2018-08-09 9:20 ` Michael S. Tsirkin
2018-08-09 9:23 ` Michael S. Tsirkin
2018-08-09 9:37 ` Peter Xu
2018-08-09 10:13 ` Michael S. Tsirkin
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