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Re: [PATCH] xen/mm: Introduce per-arch pte_attr_t type for PTE flags
- To: Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 9 Jan 2025 10:15:40 +0100
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- Cc: tpearson@xxxxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 09 Jan 2025 09:15:50 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 31.12.2024 19:27, Shawn Anastasio wrote:
> Xen's memory management APIs map_pages_to_xen, modify_xen_mappings,
> set_fixmap, ioremap_attr, and __vmap all use an unsigned int to
> represent architecture-dependent page table entry flags. This assumption
> does not work on PPC/radix where some flags go past 32-bits, so
> introduce the pte_attr_t type to allow architectures to opt in to larger
> types to store PTE flags.
>
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
As iirc Andrew had indicated when suggesting this, what you say for PPC is
true for x86 as well. Yet still we get around with unsigned int. Hence I
think the change needs describing differently.
> --- a/xen/include/xen/mm.h
> +++ b/xen/include/xen/mm.h
> @@ -70,6 +70,10 @@
> #include <xen/perfc.h>
> #include <public/memory.h>
>
> +#ifndef CONFIG_HAS_PTE_ATTR_T
> +typedef unsigned int pte_attr_t;
> +#endif
This imo makes the Kconfig control a misnomer: We'll always have pte_attr_t.
I wonder whether this actually needs a Kconfig setting in the first place:
It's hardly the end of the world for all architectures to specify the type
(later: the underlying type, for the real type to become type-safe)
explicitly.
Jan
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