Re: [PATCH v2 5/6] KVM: arm64: Use get_page() instead of kvm_get_pfn()
From: Alexandru Elisei <hidden>
Date: 2021-07-27 17:45:28
Also in:
kvm, kvmarm, linux-arm-kernel
Hi Marc, On 7/26/21 4:35 PM, Marc Zyngier wrote:
quoted hunk ↗ jump to hunk
When mapping a THP, we are guaranteed that the page isn't reserved, and we can safely avoid the kvm_is_reserved_pfn() call. Replace kvm_get_pfn() with get_page(pfn_to_page()). Signed-off-by: Marc Zyngier <maz@kernel.org> --- arch/arm64/kvm/mmu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index ebb28dd4f2c9..b303aa143592 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c@@ -840,7 +840,7 @@ transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot, *ipap &= PMD_MASK; kvm_release_pfn_clean(pfn); pfn &= ~(PTRS_PER_PMD - 1); - kvm_get_pfn(pfn); + get_page(pfn_to_page(pfn)); *pfnp = pfn; return PMD_SIZE;
I am not very familiar with the mm subsystem, but I did my best to review this change. kvm_get_pfn() uses get_page(pfn) if !PageReserved(pfn_to_page(pfn)). I looked at the documentation for the PG_reserved page flag, and for normal memory, what looked to me like the most probable situation where that can be set for a transparent hugepage was for the zero page. Looked at mm/huge_memory.c, and huge_zero_pfn is allocated via alloc_pages(__GFP_ZERO) (and other flags), which doesn't call SetPageReserved(). I looked at how a huge page can be mapped from handle_mm_fault and from khugepaged, and it also looks to like both are using using alloc_pages() to allocate a new hugepage. I also did a grep for SetPageReserved(), and there are very few places where that is called, and none looked like they have anything to do with hugepages. As far as I can tell, this change is correct, but I think someone who is familiar with mm would be better suited for reviewing this patch.