Re: [Xen-devel] [PATCH for-4.12 1/8] dom0/pvh: align allocation and mapping order to start address

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.02.19 at 18:11, <roger.pau@xxxxxxxxxx> wrote:
> On Mon, Feb 04, 2019 at 09:41:34AM -0700, Jan Beulich wrote:
>> >>> On 30.01.19 at 11:36, <roger.pau@xxxxxxxxxx> wrote:
>> > Due to the recent changes in the iommu mapping logic, the start
>> > addresses provided need to be aligned to the order intended to be
>> > mapped.
>> 
>> Irrespective of your reply to Wei's similar request (where you've
>> provided links to mails showing crashes) I'd like you to explain
>> this better. This is in particular because I don't really see what
>> "recent changes in the iommu mapping logic" you talk about.
> 
> Commit 725bf00a87f ("iommu / p2m: add a page_order parameter to
> iommu_map/unmap_page()...") added the following two asserts to
> iommu_map:
> 
> ASSERT(IS_ALIGNED(dfn_x(dfn), (1ul << page_order)));
> ASSERT(IS_ALIGNED(mfn_x(mfn), (1ul << page_order)));
> 
> Previously iommu_map would add unaligned entries without complaining,
> but now in debug builds the assert will trigger.

Right, but the assertions were added to ensure expected behavior,
not to change anything. It was a bug to call the functions without
suitably aligned frame numbers.

> Maybe adding a 'Fixes' tag would help identifying what this commit is
> trying to address?

Yes, but as per above it wouldn't be the commit adding the assertions
that the one here fixes (and hence I think the wording of the commit
message ought to change as well).

Jan



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