| Message ID | 1447164680-16330-1-git-send-email-ard.biesheuvel@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Nov 10, 2015 at 03:11:20PM +0100, Ard Biesheuvel wrote: > 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. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > Tested-by: Pavel Fedin <p.fedin@samsung.com> > Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org> Thanks, applied. -Christoffer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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
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. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Tested-by: Pavel Fedin <p.fedin@samsung.com> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org> --- Resending since I failed to cc the lists the first time around, only difference is the added tags. arch/arm/kvm/mmu.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)