From: Andrea Arcangeli Date: Thu, 25 Jul 2013 01:04:38 +0000 (+0200) Subject: kvm: optimize away THP checks in kvm_is_mmio_pfn() X-Git-Tag: v3.12-rc1~143^2~11 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=11feeb498086a3a5907b8148bdf1786a9b18fc55;p=pandora-kernel.git kvm: optimize away THP checks in kvm_is_mmio_pfn() The checks on PG_reserved in the page structure on head and tail pages aren't necessary because split_huge_page wouldn't transfer the PG_reserved bit from head to tail anyway. This was a forward-thinking check done in the case PageReserved was set by a driver-owned page mapped in userland with something like remap_pfn_range in a VM_PFNMAP region, but using hugepmds (not possible right now). It was meant to be very safe, but it's overkill as it's unlikely split_huge_page could ever run without the driver noticing and tearing down the hugepage itself. And if a driver in the future will really want to map a reserved hugepage in userland using an huge pmd it should simply take care of marking all subpages reserved too to keep KVM safe. This of course would require such a hypothetical driver to tear down the huge pmd itself and splitting the hugepage itself, instead of relaying on split_huge_page, but that sounds very reasonable, especially considering split_huge_page wouldn't currently transfer the reserved bit anyway. Signed-off-by: Andrea Arcangeli Signed-off-by: Gleb Natapov --- Reading git-diff-tree failed