linux-kernel - Re: [PATCH 0/3] intel-iommu: fix mapping PSI missing for iommu

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Message-ID: <20180418083650.GE14841@xz-mi>
Date:   Wed, 18 Apr 2018 16:36:50 +0800
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 0/3] intel-iommu: fix mapping PSI missing for iommu_map()

On Wed, Apr 18, 2018 at 12:41:27PM +0800, Peter Xu wrote:
> (PSI stands for: Page Selective Invalidations)
> 
> Intel IOMMU has the caching mode to ease emulation of the device.
> When that bit is set, we need to send PSIs even for newly mapped
> pages.  However current driver is not fully obey the rule.  E.g.,
> iommu_map() API will only do the mapping but it never sent the PSIs
> before.  That can be problematic to emulated IOMMU devices since
> they'll never be able to build up the shadow page tables if without
> such information.  This patchset tries to fix the problem.
> 
> Patch 1 is a tracing enhancement that helped me to triage the problem.
> It might even be useful in the future.
> 
> Patch 2 generalized a helper to notify the MAP PSIs.
> 
> Patch 3 fixes the real problem by making sure every domain mapping
> will trigger the MAP PSI notifications.
> 
> Without the patchset, nested device assignment (assign one device
> firstly to L1 guest, then to L2 guest) won't work for QEMU.  After
> applying the patchset, it works.
> 
> Please review.  Thanks.

I even forgot to CC iommu list.  I'll just repost.  Sorry for the
troublesome.

-- 
Peter Xu