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    SubjectRe: [PATCH 4.3 138/157] ARM/arm64: KVM: test properly for a PTEs uncachedness
    On Wed, Jan 27, 2016 at 10:13:25AM -0800, Greg Kroah-Hartman wrote:
    > 4.3-stable review patch. If anyone has any objections, please let me know.

    This patch should not be applied independently without the fix in
    mainline:

    0de58f852875a0f0dcfb120bb8433e4e73c7803b
    (ARM/arm64: KVM: correct PTE uncachedness check, 2015-12-03)

    Thanks,
    -Christoffer

    > ------------------
    >
    > From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    >
    > commit e6fab54423450d699a09ec2b899473a541f61971 upstream.
    >
    > 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>
    > Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
    > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    >
    > ---
    > arch/arm/kvm/mmu.c | 15 +++++++--------
    > 1 file changed, 7 insertions(+), 8 deletions(-)
    >
    > --- a/arch/arm/kvm/mmu.c
    > +++ b/arch/arm/kvm/mmu.c
    > @@ -98,6 +98,11 @@ static void kvm_flush_dcache_pud(pud_t p
    > __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,
    > 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
    >
    > 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 kv
    > 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
    >
    >

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