From: Lu Baolu <baolu.lu@linux.intel.com>
To: Nadav Amit <nadav.amit@gmail.com>,
"Longpeng (Mike,
Cloud Infrastructure Service Product Dept.)"
<longpeng2@huawei.com>
Cc: baolu.lu@linux.intel.com, chenjiashang <chenjiashang@huawei.com>,
"Tian, Kevin" <kevin.tian@intel.com>,
"will@kernel.org" <will@kernel.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
"Gonglei (Arei)" <arei.gonglei@huawei.com>,
David Woodhouse <dwmw2@infradead.org>
Subject: Re: A problem of Intel IOMMU hardware ?
Date: Sat, 27 Mar 2021 10:31:32 +0800 [thread overview]
Message-ID: <14fe0083-cbff-884c-34db-ce3227e026f5@linux.intel.com> (raw)
In-Reply-To: <55E334BA-C6D2-4892-9207-32654FBF4360@gmail.com>
Hi Nadav,
On 3/19/21 12:46 AM, Nadav Amit wrote:
> So here is my guess:
>
> Intel probably used as a basis for the IOTLB an implementation of
> some other (regular) TLB design.
>
> Intel SDM says regarding TLBs (4.10.4.2 “Recommended Invalidation”):
>
> "Software wishing to prevent this uncertainty should not write to
> a paging-structure entry in a way that would change, for any linear
> address, both the page size and either the page frame, access rights,
> or other attributes.”
>
>
> Now the aforementioned uncertainty is a bit different (multiple
> *valid* translations of a single address). Yet, perhaps this is
> yet another thing that might happen.
>
> From a brief look on the handling of MMU (not IOMMU) hugepages
> in Linux, indeed the PMD is first cleared and flushed before a
> new valid PMD is set. This is possible for MMUs since they
> allow the software to handle spurious page-faults gracefully.
> This is not the case for the IOMMU though (without PRI).
>
> Not sure this explains everything though. If that is the problem,
> then during a mapping that changes page-sizes, a TLB flush is
> needed, similarly to the one Longpeng did manually.
I have been working with Longpeng on this issue these days. It turned
out that your guess is right. The PMD is first cleared but not flushed
before a new valid one is set. The previous entry might be cached in the
paging structure caches hence leads to disaster.
In __domain_mapping():
2352 /*
2353 * Ensure that old small page
tables are
2354 * removed to make room for
superpage(s).
2355 * We're adding new large pages, so
make sure
2356 * we don't remove their parent tables.
2357 */
2358 dma_pte_free_pagetable(domain,
iov_pfn, end_pfn,
2359
largepage_lvl + 1);
I guess adding a cache flush operation after PMD switching should solve
the problem.
I am still not clear about this comment:
"
This is possible for MMUs since they allow the software to handle
spurious page-faults gracefully. This is not the case for the IOMMU
though (without PRI).
"
Can you please shed more light on this?
Best regards,
baolu
next prev parent reply other threads:[~2021-03-27 2:42 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-17 3:16 A problem of Intel IOMMU hardware ? Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-17 5:16 ` Lu Baolu
2021-03-17 9:40 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-17 15:18 ` Alex Williamson
2021-03-18 2:58 ` Lu Baolu
2021-03-18 4:46 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-18 7:48 ` Nadav Amit
2021-03-17 5:46 ` Nadav Amit
2021-03-17 9:35 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-17 18:12 ` Nadav Amit
2021-03-18 3:03 ` Lu Baolu
2021-03-18 8:20 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-18 8:27 ` Tian, Kevin
2021-03-18 8:38 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-18 8:43 ` Tian, Kevin
2021-03-18 8:54 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-18 8:56 ` Tian, Kevin
2021-03-18 9:25 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-18 16:46 ` Nadav Amit
2021-03-21 23:51 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-22 0:27 ` Longpeng (Mike, Cloud Infrastructure Service Product Dept.)
2021-03-27 2:31 ` Lu Baolu [this message]
2021-03-27 4:36 ` Nadav Amit
2021-03-27 5:27 ` Lu Baolu
2021-03-19 0:15 ` Lu Baolu
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