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Re: [PATCH V4] xen/gnttab: Store frame GFN in struct page_info on Arm
- To: Oleksandr <olekstysh@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 5 Jan 2022 08:30:54 +0100
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- Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Julien Grall <julien@xxxxxxx>
- Delivery-date: Wed, 05 Jan 2022 07:31:32 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 04.01.2022 22:41, Oleksandr wrote:
> On 04.01.22 10:36, Jan Beulich wrote:
>> On 22.12.2021 13:44, Oleksandr wrote:
>>> I also wonder, can we apply pattern for all type of pages here (without
>>> differentiating)?
>> I'm afraid I don't understand this part: How could we get along without
>> differentiating Xen heap and domain heap pages?
>
> I was thinking, what bad could happen if we would simply use the following:
>
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index 50334a0..97cf0d8 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -1024,7 +1024,7 @@ static struct page_info *alloc_heap_pages(
> &tlbflush_timestamp);
>
> /* Initialise fields which have other uses for free pages. */
> - pg[i].u.inuse.type_info = 0;
> + pg[i].u.inuse.type_info = PGT_TYPE_INFO_INIT_PATTERN;
> page_set_owner(&pg[i], NULL);
>
> }
>
>
> on Arm:
> #define PGT_TYPE_INFO_INIT_PATTERN PGT_gfn_mask
> or
> #define PGT_TYPE_INFO_INIT_PATTERN gfn_x(PGT_INVALID_XENHEAP_GFN)
>
> on x86:
> #define PGT_TYPE_INFO_INIT_PATTERN 0
>
>
> Yes, we apply this pattern to *all* pages, although the gfn portion is
> only used for xenheap pages.
> I might mistake but I think this pattern (which doesn't set any bits
> outside of the gfn portion) is harmless for non-xenheap pages, albeit an
> extra action.
I wouldn't mind this, but it's largely to the Arm maintainers to be
happy with it, i.e. not foreseeing present or latent issues.
Jan
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