[PATCH 4.2.y-ckt 098/305] ARM/arm64: KVM: correct PTE uncachedness check

[Kamal Mostafa]

4.2.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Ard Biesheuvel <ard.biesheuvel at linaro.org>

commit 0de58f852875a0f0dcfb120bb8433e4e73c7803b upstream.

Commit e6fab5442345 ("ARM/arm64: KVM: test properly for a PTE's
uncachedness") modified the logic to test whether a HYP or stage-2
mapping needs flushing, from [incorrectly] interpreting the page table
attributes to [incorrectly] checking whether the PFN that backs the
mapping is covered by host system RAM. The PFN number is part of the
output of the translation, not the input, so we have to use pte_pfn()
on the contents of the PTE, not __phys_to_pfn() on the HYP virtual
address or stage-2 intermediate physical address.

Fixes: e6fab5442345 ("ARM/arm64: KVM: test properly for a PTE's uncachedness")
Tested-by: Pavel Fedin <p.fedin at samsung.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm/kvm/mmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 7dace90..61d96a6 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -218,7 +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 (!kvm_is_device_pfn(__phys_to_pfn(addr)))
+			if (!kvm_is_device_pfn(pte_pfn(old_pte)))
 				kvm_flush_dcache_pte(old_pte);
 
 			put_page(virt_to_page(pte));
@@ -310,7 +310,7 @@ static void stage2_flush_ptes(struct kvm *kvm, pmd_t *pmd,
 
 	pte = pte_offset_kernel(pmd, addr);
 	do {
-		if (!pte_none(*pte) && !kvm_is_device_pfn(__phys_to_pfn(addr)))
+		if (!pte_none(*pte) && !kvm_is_device_pfn(pte_pfn(*pte)))
 			kvm_flush_dcache_pte(*pte);
 	} while (pte++, addr += PAGE_SIZE, addr != end);
 }
-- 
1.9.1