From e6fab54423450d699a09ec2b899473a541f61971 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Tue, 10 Nov 2015 15:11:20 +0100 Subject: [PATCH] ARM/arm64: KVM: test properly for a PTE's uncachedness The open coded tests for checking whether a PTE maps a page as uncached use a flawed '(pte_val(xxx) & CONST) != CONST' pattern, which is not guaranteed to work since the type of a mapping is not a set of mutually exclusive bits For HYP mappings, the type is an index into the MAIR table (i.e, the index itself does not contain any information whatsoever about the type of the mapping), and for stage-2 mappings it is a bit field where normal memory and device types are defined as follows: #define MT_S2_NORMAL 0xf #define MT_S2_DEVICE_nGnRE 0x1 I.e., masking *and* comparing with the latter matches on the former, and we have been getting lucky merely because the S2 device mappings also have the PTE_UXN bit set, or we would misidentify memory mappings as device mappings. Since the unmap_range() code path (which contains one instance of the flawed test) is used both for HYP mappings and stage-2 mappings, and considering the difference between the two, it is non-trivial to fix this by rewriting the tests in place, as it would involve passing down the type of mapping through all the functions. However, since HYP mappings and stage-2 mappings both deal with host physical addresses, we can simply check whether the mapping is backed by memory that is managed by the host kernel, and only perform the D-cache maintenance if this is the case. Cc: stable@vger.kernel.org Signed-off-by: Ard Biesheuvel Tested-by: Pavel Fedin Reviewed-by: Christoffer Dall Signed-off-by: Christoffer Dall --- arch/arm/kvm/mmu.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c index 6984342da13d..7dace909d5cf 100644 --- a/arch/arm/kvm/mmu.c +++ b/arch/arm/kvm/mmu.c @@ -98,6 +98,11 @@ static void kvm_flush_dcache_pud(pud_t pud) __kvm_flush_dcache_pud(pud); } +static bool kvm_is_device_pfn(unsigned long pfn) +{ + return !pfn_valid(pfn); +} + /** * stage2_dissolve_pmd() - clear and flush huge PMD entry * @kvm: pointer to kvm structure. @@ -213,7 +218,7 @@ static void unmap_ptes(struct kvm *kvm, pmd_t *pmd, kvm_tlb_flush_vmid_ipa(kvm, addr); /* No need to invalidate the cache for device mappings */ - if ((pte_val(old_pte) & PAGE_S2_DEVICE) != PAGE_S2_DEVICE) + if (!kvm_is_device_pfn(__phys_to_pfn(addr))) kvm_flush_dcache_pte(old_pte); put_page(virt_to_page(pte)); @@ -305,8 +310,7 @@ static void stage2_flush_ptes(struct kvm *kvm, pmd_t *pmd, pte = pte_offset_kernel(pmd, addr); do { - if (!pte_none(*pte) && - (pte_val(*pte) & PAGE_S2_DEVICE) != PAGE_S2_DEVICE) + if (!pte_none(*pte) && !kvm_is_device_pfn(__phys_to_pfn(addr))) kvm_flush_dcache_pte(*pte); } while (pte++, addr += PAGE_SIZE, addr != end); } @@ -1037,11 +1041,6 @@ static bool kvm_is_write_fault(struct kvm_vcpu *vcpu) return kvm_vcpu_dabt_iswrite(vcpu); } -static bool kvm_is_device_pfn(unsigned long pfn) -{ - return !pfn_valid(pfn); -} - /** * stage2_wp_ptes - write protect PMD range * @pmd: pointer to pmd entry -- 2.20.1