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From: Ryan Roberts <ryan.roberts@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH v1 2/2] KVM: arm64: Fix PAR_TO_HPFAR() to work independently of PA_BITS.
Date: Thu,  3 Nov 2022 15:05:07 +0000	[thread overview]
Message-ID: <20221103150507.32948-3-ryan.roberts@arm.com> (raw)
In-Reply-To: <20221103150507.32948-1-ryan.roberts@arm.com>

Kernel configs with PAGE_SIZE=64KB and PA_BITS=48 still advertise 52 bit
IPA space on HW that implements LPA. This is by design. (Admitedly this
is a very unlikely configuration in the real world).

However on such a config, attempting to create a vm with the guest
kernel placed above 48 bits in IPA space results in misbehaviour due to
the hypervisor incorrectly interpretting a faulting IPA.

Fix up PAR_TO_HPFAR() to always take 52 bits out of the PAR rather than
masking to CONFIG_ARM64_PA_BITS. If the system has a smaller implemented
PARange this should be safe because the bits are res0.

A more robust approach would be to discover the IPA size in use by the
page-table and mask based on that, to avoid relying on res0 reading back
as zero. But this information is difficult to access safely from the
code's location, so take the easy way out.

Fixes: bc1d7de8c550 ("kvm: arm64: Add 52bit support for PAR to HPFAR
conversoin")

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 arch/arm64/include/asm/kvm_arm.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
index 8aa8492dafc0..a82f2493a72b 100644
--- a/arch/arm64/include/asm/kvm_arm.h
+++ b/arch/arm64/include/asm/kvm_arm.h
@@ -340,9 +340,13 @@
  * We have
  *	PAR	[PA_Shift - 1	: 12] = PA	[PA_Shift - 1 : 12]
  *	HPFAR	[PA_Shift - 9	: 4]  = FIPA	[PA_Shift - 1 : 12]
+ *
+ * Always assume 52 bit PA since at this point, we don't know how many PA bits
+ * the page table has been set up for. This should be safe since unused address
+ * bits in PAR are res0.
  */
 #define PAR_TO_HPFAR(par)		\
-	(((par) & GENMASK_ULL(PHYS_MASK_SHIFT - 1, 12)) >> 8)
+	(((par) & GENMASK_ULL(52 - 1, 12)) >> 8)
 
 #define ECN(x) { ESR_ELx_EC_##x, #x }
 
-- 
2.17.1

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WARNING: multiple messages have this Message-ID (diff)
From: Ryan Roberts <ryan.roberts@arm.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	kvmarm@lists.cs.columbia.edu
Subject: [PATCH v1 2/2] KVM: arm64: Fix PAR_TO_HPFAR() to work independently of PA_BITS.
Date: Thu,  3 Nov 2022 15:05:07 +0000	[thread overview]
Message-ID: <20221103150507.32948-3-ryan.roberts@arm.com> (raw)
Message-ID: <20221103150507.pZHUJmk_dx4X9NPHRKWQeZ2n7zkeQ0EpvENeRjDWvMc@z> (raw)
In-Reply-To: <20221103150507.32948-1-ryan.roberts@arm.com>

Kernel configs with PAGE_SIZE=64KB and PA_BITS=48 still advertise 52 bit
IPA space on HW that implements LPA. This is by design. (Admitedly this
is a very unlikely configuration in the real world).

However on such a config, attempting to create a vm with the guest
kernel placed above 48 bits in IPA space results in misbehaviour due to
the hypervisor incorrectly interpretting a faulting IPA.

Fix up PAR_TO_HPFAR() to always take 52 bits out of the PAR rather than
masking to CONFIG_ARM64_PA_BITS. If the system has a smaller implemented
PARange this should be safe because the bits are res0.

A more robust approach would be to discover the IPA size in use by the
page-table and mask based on that, to avoid relying on res0 reading back
as zero. But this information is difficult to access safely from the
code's location, so take the easy way out.

Fixes: bc1d7de8c550 ("kvm: arm64: Add 52bit support for PAR to HPFAR
conversoin")

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 arch/arm64/include/asm/kvm_arm.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
index 8aa8492dafc0..a82f2493a72b 100644
--- a/arch/arm64/include/asm/kvm_arm.h
+++ b/arch/arm64/include/asm/kvm_arm.h
@@ -340,9 +340,13 @@
  * We have
  *	PAR	[PA_Shift - 1	: 12] = PA	[PA_Shift - 1 : 12]
  *	HPFAR	[PA_Shift - 9	: 4]  = FIPA	[PA_Shift - 1 : 12]
+ *
+ * Always assume 52 bit PA since at this point, we don't know how many PA bits
+ * the page table has been set up for. This should be safe since unused address
+ * bits in PAR are res0.
  */
 #define PAR_TO_HPFAR(par)		\
-	(((par) & GENMASK_ULL(PHYS_MASK_SHIFT - 1, 12)) >> 8)
+	(((par) & GENMASK_ULL(52 - 1, 12)) >> 8)
 
 #define ECN(x) { ESR_ELx_EC_##x, #x }
 
-- 
2.17.1


  parent reply	other threads:[~2022-11-03 15:05 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-03 15:05 [PATCH v1 0/2] KVM fixes for exotic configurations Ryan Roberts
2022-11-03 15:05 ` Ryan Roberts
2022-11-03 15:05 ` [PATCH v1 1/2] KVM: arm64: Fix kvm init failure when mode!=vhe and VA_BITS=52 Ryan Roberts
2022-11-03 15:05   ` Ryan Roberts
2022-11-03 15:05 ` Ryan Roberts [this message]
2022-11-03 15:05   ` [PATCH v1 2/2] KVM: arm64: Fix PAR_TO_HPFAR() to work independently of PA_BITS Ryan Roberts
2022-11-10 19:25 ` [PATCH v1 0/2] KVM fixes for exotic configurations Marc Zyngier
2022-11-10 19:25   ` Marc Zyngier

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