Patch "ARM/arm64: KVM: test properly for a PTE's uncachedness" has been added to the 4.3-stable tree

Patch "ARM/arm64: KVM: test properly for a PTE's uncachedness" has been added to the 4.3-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    ARM/arm64: KVM: test properly for a PTE's uncachedness

to the 4.3-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arm-arm64-kvm-test-properly-for-a-pte-s-uncachedness.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From e6fab54423450d699a09ec2b899473a541f61971 Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date: Tue, 10 Nov 2015 15:11:20 +0100
Subject: ARM/arm64: KVM: test properly for a PTE's uncachedness

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


Patches currently in stable-queue which might be from ard.biesheuvel@linaro.org are

queue-4.3/arm-arm64-kvm-test-properly-for-a-pte-s-uncachedness.patch
queue-4.3/arm64-mm-use-correct-mapping-granularity-under-debug_rodata.patch
queue-4.3/arm-arm64-kvm-correct-pte-uncachedness-check.patch