From: Julien Grall Date: Sat, 20 Feb 2021 17:54:13 +0000 (+0000) Subject: xen/arm: mm: flush_page_to_ram() only need to clean to PoC X-Git-Tag: archive/raspbian/4.16.0+51-g0941d6cb-1+rpi1~2^2~42^2~772 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=9617d5f9c19d1d157629e1e436791509526e0ce5;p=xen.git xen/arm: mm: flush_page_to_ram() only need to clean to PoC At the moment, flush_page_to_ram() is both cleaning and invalidate to PoC the page. The goal of flush_page_to_ram() is to prevent corruption when the guest has disabled the cache (the cache line may be dirty) and the guest to read previous content. Per this definition, the invalidating the line is not necessary. So invalidating the cache is unnecessary. In fact, it may be counter- productive as the line may be (speculatively) accessed a bit after. So this will incurr an expensive access to the memory. More generally, we should avoid interferring too much with cache. Therefore, flush_page_to_ram() is updated to only clean to PoC the page. The performance impact of this change will depend on your workload/processor. Signed-off-by: Julien Grall Reviewed-by: Bertrand Marquis Acked-by: Stefano Stabellini --- diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index 59f8a3f15f..2f11d214e1 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); /*