Patchwork kvm: arm: Skip stage2 huge mappings for unaligned ipa backed by THP

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Submitter Suzuki K Poulose
Date April 2, 2019, 11:06 a.m.
Message ID <1554203176-3958-1-git-send-email-suzuki.poulose@arm.com>
Download mbox | patch
Permalink /patch/763541/
State New
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Comments

Suzuki K Poulose - April 2, 2019, 11:06 a.m.
With commit a80868f398554842b14, we no longer ensure that the
THP page is properly aligned in the guest IPA. Skip the stage2
huge mapping for unaligned IPA backed by transparent hugepages.

Fixes: a80868f398554842b14 ("KVM: arm/arm64: Enforce PTE mappings at stage2 when needed")
Reported-by: Eric Auger <eric.auger@redhat.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Chirstoffer Dall <christoffer.dall@arm.com>
Cc: Zenghui Yu <yuzenghui@huawei.com>
Cc: Zheng Xiang <zhengxiang9@huawei.com>
Tested-by: Eric Auger <eric.auger@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 virt/kvm/arm/mmu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
Andrew Murray - April 2, 2019, 3:53 p.m.
On Tue, Apr 02, 2019 at 12:06:16PM +0100, Suzuki K Poulose wrote:
> With commit a80868f398554842b14, we no longer ensure that the
> THP page is properly aligned in the guest IPA. Skip the stage2
> huge mapping for unaligned IPA backed by transparent hugepages.
> 
> Fixes: a80868f398554842b14 ("KVM: arm/arm64: Enforce PTE mappings at stage2 when needed")
> Reported-by: Eric Auger <eric.auger@redhat.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Chirstoffer Dall <christoffer.dall@arm.com>
> Cc: Zenghui Yu <yuzenghui@huawei.com>
> Cc: Zheng Xiang <zhengxiang9@huawei.com>
> Tested-by: Eric Auger <eric.auger@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
>  virt/kvm/arm/mmu.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index 27c9583..4a22f5b 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c
> @@ -1412,7 +1412,9 @@ static bool transparent_hugepage_adjust(kvm_pfn_t *pfnp, phys_addr_t *ipap)
>  		 * page accordingly.
>  		 */
>  		mask = PTRS_PER_PMD - 1;
> -		VM_BUG_ON((gfn & mask) != (pfn & mask));
> +		/* Skip memslots with unaligned IPA and user address */
> +		if ((gfn & mask) != (pfn & mask))
> +			return false;
>  		if (pfn & mask) {
>  			*ipap &= PMD_MASK;
>  			kvm_release_pfn_clean(pfn);
> -- 
> 2.7.4

I was able to reproduce this issue on v5.1-rc3 on a SoftIron Overdrive 1000
(AMD Seattle (Rev.B1)) with defconfig+ARM64_64K_PAGES with:

qemu-system-aarch64 -cpu host -machine type=virt,accel=kvm -nographic -smp 4
-m 4096 -kernel /boot/vmlinuz-4.9.0-7-arm64 --append "console=ttyAMA0
default_hugepagesz=2M hugepages=256"

The 'default_hugepagesz=2M hugepages=256' had no effect on the reproducibility,
however the guest only intermittently failed to boot. Applying the above
patch fixed this and the guest boots every time.

Tested-by: Andrew Murray <andrew.murray@arm.com>

Thanks,

Andrew Murray

> 
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> kvmarm@lists.cs.columbia.edu
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Patch

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 27c9583..4a22f5b 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1412,7 +1412,9 @@  static bool transparent_hugepage_adjust(kvm_pfn_t *pfnp, phys_addr_t *ipap)
 		 * page accordingly.
 		 */
 		mask = PTRS_PER_PMD - 1;
-		VM_BUG_ON((gfn & mask) != (pfn & mask));
+		/* Skip memslots with unaligned IPA and user address */
+		if ((gfn & mask) != (pfn & mask))
+			return false;
 		if (pfn & mask) {
 			*ipap &= PMD_MASK;
 			kvm_release_pfn_clean(pfn);