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authorCatalin Marinas <catalin.marinas@arm.com>2016-04-13 17:57:37 +0100
committerChristoffer Dall <christoffer.dall@linaro.org>2016-05-09 22:23:08 +0200
commit06485053244480f5f403d8f89b8617bd7d549113 (patch)
tree4f1ef376aae6b679b941230953e8be8f801bed06 /.get_maintainer.ignore
parenta53d892dfb6f14f77c508e1027f5e1bdb400fd23 (diff)
downloadlinux-06485053244480f5f403d8f89b8617bd7d549113.tar.gz
kvm: arm64: Enable hardware updates of the Access Flag for Stage 2 page tables
The ARMv8.1 architecture extensions introduce support for hardware updates of the access and dirty information in page table entries. With VTCR_EL2.HA enabled (bit 21), when the CPU accesses an IPA with the PTE_AF bit cleared in the stage 2 page table, instead of raising an Access Flag fault to EL2 the CPU sets the actual page table entry bit (10). To ensure that kernel modifications to the page table do not inadvertently revert a bit set by hardware updates, certain Stage 2 software pte/pmd operations must be performed atomically. The main user of the AF bit is the kvm_age_hva() mechanism. The kvm_age_hva_handler() function performs a "test and clear young" action on the pte/pmd. This needs to be atomic in respect of automatic hardware updates of the AF bit. Since the AF bit is in the same position for both Stage 1 and Stage 2, the patch reuses the existing ptep_test_and_clear_young() functionality if __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG is defined. Otherwise, the existing pte_young/pte_mkold mechanism is preserved. The kvm_set_s2pte_readonly() (and the corresponding pmd equivalent) have to perform atomic modifications in order to avoid a race with updates of the AF bit. The arm64 implementation has been re-written using exclusives. Currently, kvm_set_s2pte_writable() (and pmd equivalent) take a pointer argument and modify the pte/pmd in place. However, these functions are only used on local variables rather than actual page table entries, so it makes more sense to follow the pte_mkwrite() approach for stage 1 attributes. The change to kvm_s2pte_mkwrite() makes it clear that these functions do not modify the actual page table entries. The (pte|pmd)_mkyoung() uses on Stage 2 entries (setting the AF bit explicitly) do not need to be modified since hardware updates of the dirty status are not supported by KVM, so there is no possibility of losing such information. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Acked-by: Marc Zyngier <marc.zyngier@arm.com> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
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