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Re: [Xen-devel] [PATCH] vunmap: let vunmap align virtual address by itself
- To: Julien Grall <julien.grall@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrii Anisov <andrii.anisov@xxxxxxxxx>
- Date: Mon, 22 Jul 2019 12:12:04 +0300
- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Andrii Anisov <andrii_anisov@xxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 22 Jul 2019 09:12:14 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 19.07.19 12:51, Julien Grall wrote:
Currently vunmap() is called from from xen/arch/arm/cpuerrata.c with an
s/ from//
address potentially not page aligned. Instead of fixing that in ARM code,
s/ARM/Arm/
we let vunmap() making alignment by itself and stripping other existing
vunmap() calls from prior masking. This makes it consistent with how
{,un}map_domain_page() currently works.
The commit message does not state what could goes wrong if the page is not
aligned. So how about:
Since commit 9cc0618eb0 "xen/arm: mm: Sanity check any update of Xen page
tables", the MM code requires the virtual address to be page-aligned. As the
vunmap() helper is directly used the virtual address passed by its caller, this now
implies the caller should pass a page-aligned virtual address.
One of the caller in xen/arch/arm/cpuerrata.c may actually pass an unaligned
address resulting the vunmap() to silently fail and potentially making future
user of vmap() to fail (the MM code does not allow to replace existing mapping).
In general, it would be better to have vunmap() more resilient to unaligned
address. So the function is now page-aligning the virtual address.
Note that for multi-pages virtual mapping, the address should still point into
the first page. Otherwise, vunmap() may only partially remove the mapping.
I'm ok with that.
Why did you remove the following line:
- strip all existing vunmap() calls from prior masking
Because I already mentioned it in the main body of my message.
address potentially not page aligned. Instead of fixing that in ARM code,
we let vunmap() making alignment by itself and stripping other existing
vunmap() calls from prior masking.
Yet, with your text both notes are needed.
--
Sincerely,
Andrii Anisov.
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