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authorAndrea Arcangeli <aarcange@redhat.com>2013-07-25 03:04:38 +0200
committerGleb Natapov <gleb@redhat.com>2013-08-27 11:01:10 +0300
commit11feeb498086a3a5907b8148bdf1786a9b18fc55 (patch)
tree9dcef9a577fd410f84f42b972e2fd4e1ff46f68c /net/sysctl_net.c
parent0bd50dc971aad3c29043de4fb7bce45c351d1b67 (diff)
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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 <aarcange@redhat.com> Signed-off-by: Gleb Natapov <gleb@redhat.com>
Diffstat (limited to 'net/sysctl_net.c')
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