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Re: [Xen-devel] [PATCH] vunmap: let vunmap align virtual address by itself


  • To: Andrii Anisov <andrii.anisov@xxxxxxxxx>
  • From: Jan Beulich <JBeulich@xxxxxxxx>
  • Date: Tue, 23 Jul 2019 09:12:31 +0000
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  • 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>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Tue, 23 Jul 2019 09:14:41 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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  • Thread-topic: [PATCH] vunmap: let vunmap align virtual address by itself

On 23.07.2019 10:48, Andrii Anisov wrote:
> Julien, Jan, Andrew,
> 
> The problem addressed by [1] causes random ARM64 boot fails dependent on 
> hypervisor code changes.
> Yet more generic solution was requested by Andrew and supported by Julien [2].
> 
> How to proceed with this particular patch?
> As I understand, Jan doubts we should move page alignment to vunmap(), while 
> Julien and Andrew wanted the commit message clarification.
> Can we have an agreement on approach here?
> 
> [1] https://lists.xenproject.org/archives/html/xen-devel/2019-07/msg01167.html
> [2] https://lists.xenproject.org/archives/html/xen-devel/2019-07/msg01129.html

First of all, let me quote Linux'es code:

static void __vunmap(const void *addr, int deallocate_pages)
{
        struct vm_struct *area;

        if (!addr)
                return;

        if (WARN(!PAGE_ALIGNED(addr), "Trying to vfree() bad address (%p)\n",
                        addr))
                return;

As long as we aim to have a reasonable level of compatibility of
similar interfaces, we should not go the suggested route.

Beyond that I continue to be of the opinion that it should be
all-or-nothing: Any pointer pointing anywhere at or inside the
region should be accepted, or just the one pointing precisely at
the start.

Jan
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