Re: [PATCH] KVM: arm64: Restrict IPA size to maximum 48 bits on 4K and 16K page size

On 8/11/21 3:06 PM, Marc Zyngier wrote:

On Wed, 11 Aug 2021 05:52:29 +0100,
Anshuman Khandual [off-list ref] wrote:

quoted

Even though ID_AA64MMFR0.PARANGE reports 52 bit PA size support, it cannot
be enabled as guest IPA size on 4K or 16K page size configurations. Hence
kvm_ipa_limit must be restricted to 48 bits. This change achieves required
IPA capping.

Before the commit c9b69a0cf0b4 ("KVM: arm64: Don't constrain maximum IPA
size based on host configuration"), the problem here would have been just
latent via PHYS_MASK_SHIFT (which earlier in turn capped kvm_ipa_limit),
which remains capped at 48 bits on 4K and 16K configs.

Cc: Marc Zyngier <maz@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Alexandru Elisei <redacted>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: kvmarm@lists.cs.columbia.edu
Cc: linux-kernel@vger.kernel.org
Fixes: c9b69a0cf0b4 ("KVM: arm64: Don't constrain maximum IPA size based on host configuration")
Signed-off-by: Anshuman Khandual <redacted>
---
This applies on v5.14-rc5

 arch/arm64/kvm/reset.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 20588220fe66..e66974c4b9d3 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c

@@ -337,6 +337,15 @@ int kvm_set_ipa_limit(void)
 		return -EINVAL;
 	}
 
+	/*
+	 * IPA size beyond 48 bits could not be supported
+	 * on either 4K or 16K page size. Hence let's cap
+	 * it to 48 bits, in case it's reported as larger
+	 * on the system.
+	 */
+	if (!IS_ENABLED(CONFIG_ARM64_64K_PAGES))

As per our earlier discussion, please use (PAGE_SIZE != SZ_64K)
instead. This is in keeping with the rest of the file.

Sure, will change.

quoted

+		parange = min(parange, (unsigned int)ID_AA64MMFR0_PARANGE_48);
+

Also, please move it next to the point where we assign parange.

Sure, will move.

quoted

 	kvm_ipa_limit = id_aa64mmfr0_parange_to_phys_shift(parange);
 	kvm_info("IPA Size Limit: %d bits%s\n", kvm_ipa_limit,
 		 ((kvm_ipa_limit < KVM_PHYS_SHIFT) ?

Thanks,

	M.

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