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From: Wei Liu <wei.liu@kernel.org>
To: Praveen Kumar <kumarpraveen@linux.microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>,
	Linux on Hyper-V List <linux-hyperv@vger.kernel.org>,
	virtualization@lists.linux-foundation.org,
	Linux Kernel List <linux-kernel@vger.kernel.org>,
	Michael Kelley <mikelley@microsoft.com>,
	Vineeth Pillai <viremana@linux.microsoft.com>,
	Sunil Muthuswamy <sunilmut@microsoft.com>,
	Nuno Das Neves <nunodasneves@linux.microsoft.com>,
	pasha.tatashin@soleen.com, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Dexuan Cui <decui@microsoft.com>,
	"open list:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>
Subject: Re: [RFC v1 5/8] mshv: add paravirtualized IOMMU support
Date: Tue, 10 Aug 2021 10:46:58 +0000	[thread overview]
Message-ID: <20210810104658.5ir7cibalhy3roun@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <562f4c31-1ea5-ea56-ac0a-6bd80b61c3df@linux.microsoft.com>

On Wed, Aug 04, 2021 at 12:13:42PM +0530, Praveen Kumar wrote:
> On 04-08-2021 03:17, Wei Liu wrote:
> >>> +static size_t hv_iommu_unmap(struct iommu_domain *d, unsigned long iova,
> >>> +			   size_t size, struct iommu_iotlb_gather *gather)
> >>> +{
> >>> +	size_t unmapped;
> >>> +	struct hv_iommu_domain *domain = to_hv_iommu_domain(d);
> >>> +	unsigned long flags, npages;
> >>> +	struct hv_input_unmap_device_gpa_pages *input;
> >>> +	u64 status;
> >>> +
> >>> +	unmapped = hv_iommu_del_mappings(domain, iova, size);
> >>> +	if (unmapped < size)
> >>> +		return 0;
> >> Is there a case where unmapped > 0 && unmapped < size ?
> >>
> > There could be such a case -- hv_iommu_del_mappings' return value is >= 0.
> > Is there a problem with this predicate?
> 
> What I understand, if we are unmapping and return 0, means nothing was
> unmapped, and will that not cause any corruption or illegal access of
> unmapped memory later?  From __iommu_unmap

Those pages are not really unmapped. The hypercall is skipped.

> ...
>     13         while (unmapped < size) {
>     12                 size_t pgsize = iommu_pgsize(domain, iova, size - unmapped);
>     11
>     10                 unmapped_page = ops->unmap(domain, iova, pgsize, iotlb_gather);
>      9                 if (!unmapped_page)
>      8                         break;		<<< we just break here, thinking there is nothing unmapped, but actually hv_iommu_del_mappings has removed some pages.
>      7
>      6                 pr_debug("unmapped: iova 0x%lx size 0x%zx\n",
>      5                         ¦iova, unmapped_page);
>      4
>      3                 iova += unmapped_page;
>      2                 unmapped += unmapped_page;
>      1         }
> ...
> 
> Am I missing something ?
> 
> Regards,
> 
> ~Praveen.

  reply	other threads:[~2021-08-10 10:47 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-09 11:43 [RFC v1 0/8] MSHV: add PV-IOMMU driver Wei Liu
2021-07-09 11:43 ` [RFC v1 1/8] x86/hyperv: export hv_build_pci_dev_id Wei Liu
2021-07-09 11:43 ` [RFC v1 2/8] asm-generic/hyperv: add device domain definitions Wei Liu
2021-07-09 11:43 ` [RFC v1 3/8] intel/vt-d: make DMAR table parsing code more flexible Wei Liu
2021-07-09 12:56   ` Robin Murphy
2021-07-09 13:42     ` Wei Liu
2021-07-09 11:43 ` [RFC v1 4/8] intel/vt-d: export intel_iommu_get_resv_regions Wei Liu
2021-07-09 14:17   ` Lu Baolu
2021-07-09 14:21     ` Wei Liu
2021-07-09 11:43 ` [RFC v1 5/8] mshv: add paravirtualized IOMMU support Wei Liu
2021-08-03 18:40   ` Praveen Kumar
2021-08-03 21:47     ` Wei Liu
2021-08-04  6:43       ` Praveen Kumar
2021-08-10 10:46         ` Wei Liu [this message]
2021-07-09 11:43 ` [RFC v1 6/8] mshv: command line option to skip devices in PV-IOMMU Wei Liu
2021-07-09 12:46   ` Robin Murphy
2021-07-09 13:34     ` Wei Liu
2021-08-03 18:50   ` Praveen Kumar
2021-08-03 21:56     ` Wei Liu
2021-08-04  7:03       ` Praveen Kumar
2021-08-10 10:04         ` Wei Liu
2021-07-09 11:43 ` [RFC v1 7/8] mshv: implement in-kernel device framework Wei Liu
2021-07-09 13:02   ` Matthew Wilcox
2021-07-09 13:50     ` Wei Liu
2021-07-09 15:32       ` Matthew Wilcox
2021-07-09 16:27         ` Wei Liu
2021-07-09 16:38           ` Matthew Wilcox
2021-07-09 19:14             ` Wei Liu
2021-07-09 19:48               ` Matthew Wilcox
2021-07-09 20:11                 ` Wei Liu
2021-08-03 19:12   ` Praveen Kumar
2021-08-03 22:04     ` Wei Liu
2021-07-09 11:43 ` [RFC v1 8/8] mshv: add vfio bridge device Wei Liu
2021-08-03 19:27   ` Praveen Kumar
2021-08-10 10:52     ` Wei Liu

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