From: Peter Xu <peterx@redhat.com>
To: Auger Eric <eric.auger@redhat.com>
Cc: pbonzini@redhat.com, Yan Zhao <yan.y.zhao@intel.com>,
qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] memory: do not do out of bound notification
Date: Thu, 20 Jun 2019 12:02:30 +0800 [thread overview]
Message-ID: <20190620040230.GB9073@xz-x1> (raw)
In-Reply-To: <39c4c32b-e34a-8d8f-abbc-ab346ec5bed7@redhat.com>
On Wed, Jun 19, 2019 at 03:17:41PM +0200, Auger Eric wrote:
> Hi Yan,
>
> [+ Peter]
>
> On 6/19/19 10:49 AM, Yan Zhao wrote:
> > even if an entry overlaps with notifier's range, should not map/unmap
> > out of bound part in the entry.
>
> I don't think the patch was based on the master as the trace at the very
> end if not part of the upstream code.
> >
> > This would cause problem in below case:
> > 1. initially there are two notifiers with ranges
> > 0-0xfedfffff, 0xfef00000-0xffffffffffffffff,
> > IOVAs from 0x3c000000 - 0x3c1fffff is in shadow page table.
> >
> > 2. in vfio, memory_region_register_iommu_notifier() is followed by
> > memory_region_iommu_replay(), which will first call address space unmap,
> > and walk and add back all entries in vtd shadow page table. e.g.
> > (1) for notifier 0-0xfedfffff,
> > IOVAs from 0 - 0xffffffff get unmapped,
> > and IOVAs from 0x3c000000 - 0x3c1fffff get mapped
>
> While the patch looks sensible, the issue is the notifier scope used in
> vtd_address_space_unmap is not a valid mask (ctpop64(size) != 1). Then
> the size is recomputed (either using n = 64 - clz64(size) for the 1st
> notifier or n = s->aw_bits for the 2d) and also the entry (especially
> for the 2d notifier where it becomes 0) to get a proper alignment.
>
> vtd_page_walk sends notifications per block or page (with valid
> addr_mask) so stays within the notifier.
>
> Modifying the entry->iova/addr_mask again in memory_region_notify_one
> leads to unaligned start address / addr_mask. I don't think we want that.
>
> Can't we modity the vtd_address_space_unmap() implementation to split
> the invalidation in smaller chunks instead?
Seems workable, to be explicit - we can even cut it into chunks with
different size to be efficient. Like, this range:
0x0e00_0000 - 0x1_0000_0000 (size 0xf200_0000)
can be one of this:
0x0e000000 - 0x1000_0000 (size 0x0200_0000)
plus one of this:
0x1000_0000 - 0x1_0000_0000 (size 0xf000_0000)
Yan, could you help explain the issue better on how to reproduce and
what's the error when the problem occurs? For example, is that
happened when a device hot-plugged into an existing VFIO container
(with some mapped IOVAs)? Did you get host DMA errors later on?
Thanks,
--
Peter Xu
next prev parent reply other threads:[~2019-06-20 4:16 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-19 8:49 [Qemu-devel] [PATCH] memory: do not do out of bound notification Yan Zhao
2019-06-19 13:17 ` Auger Eric
2019-06-20 1:46 ` Yan Zhao
2019-06-20 4:02 ` Peter Xu [this message]
2019-06-20 4:14 ` Yan Zhao
2019-06-20 8:14 ` Peter Xu
2019-06-20 8:13 ` Yan Zhao
2019-06-20 8:35 ` Paolo Bonzini
2019-06-20 10:57 ` Yan Zhao
2019-06-20 12:04 ` Paolo Bonzini
2019-06-20 12:59 ` Peter Xu
2019-06-20 13:04 ` Peter Xu
2019-06-24 5:22 ` Yan Zhao
2019-06-24 6:14 ` Peter Xu
2019-06-20 13:14 ` Paolo Bonzini
2019-06-21 2:36 ` Peter Xu
2019-06-21 7:57 ` Yan Zhao
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