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From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Juergen Gross <jgross@suse.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Sander Eikelenboom <linux@eikelenboom.it>
Subject: Re: [Xen-devel] [PATCH 1/3] AMD/IOMMU: don't needlessly trigger errors/crashes when unmapping a page
Date: Thu, 7 Nov 2019 11:13:44 +0100	[thread overview]
Message-ID: <e9a13cff-0a01-b3f0-375f-0d92e4579130@suse.com> (raw)
In-Reply-To: <60e91912-1271-8b85-a11a-ed7f58366d1c@citrix.com>

On 06.11.2019 18:12, Andrew Cooper wrote:
> On 06/11/2019 15:18, Jan Beulich wrote:
>> Unmapping a page which has never been mapped should be a no-op (note how
>> it already is in case there was no root page table allocated).
> 
> Which function are you talking about here?  iommu_pde_from_dfn() will
> BUG() if no root was set up.

amd_iommu_unmap_page() has such a check first thing.

>> There's
>> in particular no need to grow the number of page table levels in use,
>> and there's also no need to allocate intermediate page tables except
>> when needing to split a large page.
> 
> To be honest, I've never been convinced that dynamically changing the
> number of levels in the AMD IOMMU tables is clever.  It should be fixed
> at 4 (like everything else) and suddenly a lot of runtime complexity
> disappears.  (I'm fairly confident that we'll need a domain create
> parameter to support 5 level paging in a rational way, so we won't even
> include walk-length gymnastics then either.)

5-level paging for the CPU 1st-stage-translation is imo pretty orthogonal
to needing 5 levels of paging for 2nd-stage-translation (which also is
what the IOMMU code here is about).

>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

Thanks, Jan

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  reply	other threads:[~2019-11-07 10:14 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-06 15:16 [Xen-devel] [PATCH 0/3] AMD/IOMMU: re-work mode updating Jan Beulich
2019-11-06 15:18 ` [Xen-devel] [PATCH 1/3] AMD/IOMMU: don't needlessly trigger errors/crashes when unmapping a page Jan Beulich
2019-11-06 17:12   ` Andrew Cooper
2019-11-07 10:13     ` Jan Beulich [this message]
2019-11-07 12:04   ` Paul Durrant
2019-11-12  9:59   ` Jürgen Groß
2019-11-06 15:19 ` [Xen-devel] [PATCH 2/3] introduce GFN notification for translated domains Jan Beulich
2019-11-07 11:35   ` George Dunlap
2019-11-07 11:47     ` Jan Beulich
2019-11-07 12:10       ` George Dunlap
2019-11-07 12:45         ` Jan Beulich
2019-11-06 15:19 ` [Xen-devel] [PATCH 3/3] AMD/IOMMU: use notify_dfn() hook to update paging mode Jan Beulich
2019-11-06 17:31 ` [Xen-devel] [PATCH 0/3] AMD/IOMMU: re-work mode updating Andrew Cooper
2019-11-07  7:36   ` Jan Beulich
2019-11-07 12:49     ` Andrew Cooper
2019-11-07 13:17       ` Jan Beulich
2019-11-06 18:29 ` Sander Eikelenboom
2019-11-07  7:32   ` Jan Beulich

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