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Re: [PATCH 2/2] make ioremap_wc() x86 only (for the time being)
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 30 Mar 2026 16:28:45 +0200
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- Cc: Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 30 Mar 2026 14:28:51 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.03.2026 16:24, Oleksii Kurochko wrote:
>
>
> On 3/30/26 4:22 PM, Oleksii Kurochko wrote:
>>
>>
>> On 2/19/26 4:53 PM, Jan Beulich wrote:
>>> Its use in domain building is questionable: Already at the point both
>>> uses
>>> were introduced, ioremap_cache() existed. I can't see why kernel and
>>> initrd would need mapping WC, when at the same time other similar
>>> mappings
>>> (in common/device-tree/) are done WB.
>>>
>>> With those uses replaced, neither Arm nor RISC-V have a need for the
>>> function anymore.
>>>
>>
>> It is okay for RISC-V, but for Arm, IIRC, likely it was done because
>> guest might start with cache disabled and PAGE_HYPERVISOR_WC on Arm uses
>> "Normal Non-cacheable" what could lead to that guest won't see some part
>> of kernel and/or initrd as it could be in a cache and won't be flushed
>> to RAM.
>>
>> But probably I misremembered something and
>> clean_and_invalidate_dcache_va_range() or something similar should be
>> called before guest is laucned.
>
> okay, so for this case copy_to_guest_phys_flush_dcache() is called after
> initrd and kernel are loaded.
>
> Then it looks okay to me for Arm too.
May I ask whether that removes the RISC-V restriction on the R-b (thanks
for that) you gave in the earlier reply?
Jan
|
