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Re: [PATCH for-next] xen/arm: mm: flush_page_to_ram() only need to clean to PoC
- To: Julien Grall <julien@xxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Mon, 22 Feb 2021 11:58:33 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
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- Thread-topic: [PATCH for-next] xen/arm: mm: flush_page_to_ram() only need to clean to PoC
Hi Julien,
> On 20 Feb 2021, at 17:54, Julien Grall <julien@xxxxxxx> wrote:
>
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> At the moment, flush_page_to_ram() is both cleaning and invalidate to
> PoC the page. However, the cache line can be speculated and pull in the
> cache right after as it is part of the direct map.
If we go further through this logic maybe all calls to
clean_and_invalidate_dcache_va_range could be transformed in a
clean_dcache_va_range.
>
> So it is pointless to try to invalidate the line in the data cache.
>
But what about processors which would not speculate ?
Do you expect any performance optimization here ?
If so it might be good to explain it as I am not quite sure I get it.
Cheers
Bertrand
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> ---
> xen/arch/arm/mm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 59f8a3f15fd1..2f11d214e184 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -529,7 +529,7 @@ void flush_page_to_ram(unsigned long mfn, bool
> sync_icache)
> {
> void *v = map_domain_page(_mfn(mfn));
>
> - clean_and_invalidate_dcache_va_range(v, PAGE_SIZE);
> + clean_dcache_va_range(v, PAGE_SIZE);
> unmap_domain_page(v);
>
> /*
> --
> 2.17.1
>
>
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