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Re: [PATCH v2 6/8] xen/riscv: introduce generic Xen page table handling
- To: Julien Grall <julien@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 22 Jul 2024 08:59:44 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 22 Jul 2024 06:59:56 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.07.2024 11:02, Julien Grall wrote:
> Hi,
>
> On 12/07/2024 17:22, Oleksii Kurochko wrote:
>> At least, between Arm and RISC-V most of the code related to Xen page
>> table handling are common.
>>
>> This GENERIC_PT code is based on Arm's arm/mmu/pt.c except some minor
>> changes such as introduction of the following functions:
>> * get_root_page()
>> * xen_pt_check_contig()
>> * set_pte_table_bit()
>> * sanity_arch_specific_pte_checks()
>> * get_contig_bit()
>> * set_pte_permissions()
>> * flush_xen_tlb_range_va()
>> It was done because not every functions has the generic pte_flags and
>> it could be a different positions of the PTE bits in a PTE.
> While I am always in favor of trying to avoid code duplication, I am not
> sure the page-tables are one that should be.
>
> For instance, you don't have the concept of contiguous page in RISC-V (I
> see you introduce dummy flags, but IMHO this is a bit of a hack). All
> the code was also written in a way to avoid temporary conflict mappings.
> This is to avoid using Break-Before-Make. But on newer hardware this
> could be relaxed.
>
> I am interested to know what the others thinks.
I share the concern; I was rather surprised to see the title, but - not
having had the time to look at the patch yet - was kind of guessing
(hoping) it wasn't really what the title said. Page table handling quite
likely wants to remain arch-specific.
Jan
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