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Re: [PATCH v4 2/7] xen/riscv: set up fixmap mappings
- To: oleksii.kurochko@xxxxxxxxx
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 14 Aug 2024 17:08:29 +0200
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- Cc: Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 14 Aug 2024 15:08:44 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 14.08.2024 16:21, oleksii.kurochko@xxxxxxxxx wrote:
> On Tue, 2024-08-13 at 10:22 +0200, Jan Beulich wrote:
>> On 09.08.2024 18:19, Oleksii Kurochko wrote:
>>> --- a/xen/arch/riscv/include/asm/page.h
>>> +++ b/xen/arch/riscv/include/asm/page.h
>>> @@ -81,6 +81,12 @@ static inline void flush_page_to_ram(unsigned
>>> long mfn, bool sync_icache)
>>> BUG_ON("unimplemented");
>>> }
>>>
>>> +/* Write a pagetable entry. */
>>> +static inline void write_pte(pte_t *p, pte_t pte)
>>> +{
>>> + *p = pte;
>>> +}
>>
>> No use of write_atomic() here? And no read_pte() counterpart right
>> away (then
>> also properly using read_atomic())?
> I wanted to avoid the fence before "*p=pte" which in case of
> write_atomic() will be present.
Well, this goes back to write_atomic() resolving to write{b,w,l,q}() for
unclear reasons; even the comment in our atomic.h says "For some reason".
The fence there is of course getting in the way here. I keep forgetting
about that aspect, because neither x86 nor Arm has anything similar
afaics.
> Won't it be enough to use here WRITE_ONCE()?
Maybe. I'm not entirely sure.
Jan
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