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SubjectRe: [PATCH v3 19/20] kvm: arm64: Allow IPA size supported by the system
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On 29/06/18 12:15, Suzuki K Poulose wrote:
> So far we have restricted the IPA size of the VM to the default
> value (40bits). Now that we can manage the IPA size per VM and
> support dynamic stage2 page tables, allow VMs to have larger IPA.
> This is done by setting the IPA limit to the one supported by
> the hardware and kernel. This patch also moves the check for
> the default IPA size support to kvm_get_ipa_limit().
>
> Since the stage2 page table code is dependent on the stage1
> page table, we always ensure that :
>
> Number of Levels at Stage1 >= Number of Levels at Stage2
>
> So we limit the IPA to make sure that the above condition
> is satisfied. This will affect the following combinations
> of VA_BITS and IPA for different page sizes.
>
> 39bit VA, 4K - IPA > 43 (Upto 48)
> 36bit VA, 16K - IPA > 40 (Upto 48)
> 42bit VA, 64K - IPA > 46 (Upto 52)

I'm not sure I get it. Are these the IPA sizes that we forbid based on
the host VA size and page size configuration? If so, can you rewrite
this as:

host configuration | unsupported IPA range
39bit VA, 4k | [44, 48]
36bit VA, 16K | [41, 48]
42bit VA, 64k | [47, 52]

and say that all the other combinations are supported?

>
> Supporting the above combinations need independent stage2
> page table manipulation code, which would need substantial
> changes. We could purse the solution independently and
> switch the page table code once we have it ready.
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Christoffer Dall <cdall@kernel.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> Changes since V2:
> - Restrict the IPA size to limit the number of page table
> levels in stage2 to that of stage1 or less.
> ---
> arch/arm64/include/asm/kvm_host.h | 6 ------
> arch/arm64/include/asm/kvm_mmu.h | 37 ++++++++++++++++++++++++++++++++++++-
> 2 files changed, 36 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 9a15860..e858e49 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -452,13 +452,7 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
>
> static inline void __cpu_init_stage2(void)
> {
> - u32 ps;
> -
> kvm_call_hyp(__init_stage2_translation);
> - /* Sanity check for minimum IPA size support */
> - ps = id_aa64mmfr0_parange_to_phys_shift(read_sysreg(id_aa64mmfr0_el1) & 0x7);
> - WARN_ONCE(ps < 40,
> - "PARange is %d bits, unsupported configuration!", ps);
> }
>
> /* Guest/host FPSIMD coordination helpers */
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index a291cdc..d38f395 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -547,7 +547,42 @@ static inline void *stage2_alloc_pgd(struct kvm *kvm)
>
> static inline u32 kvm_get_ipa_limit(void)
> {
> - return KVM_PHYS_SHIFT;
> + unsigned int ipa_max, va_max, parange;
> +
> + parange = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1) & 0x7;
> + ipa_max = id_aa64mmfr0_parange_to_phys_shift(parange);
> +
> + /* Raise the limit to the default size for backward compatibility */
> + if (ipa_max < KVM_PHYS_SHIFT) {
> + WARN_ONCE(1,
> + "PARange is %d bits, unsupported configuration!",
> + ipa_max);
> + ipa_max = KVM_PHYS_SHIFT;
> + }
> +
> + /* Clamp it to the PA size supported by the kernel */
> + ipa_max = (ipa_max > PHYS_MASK_SHIFT) ? PHYS_MASK_SHIFT : ipa_max;
> + /*
> + * Since our stage2 table is dependent on the stage1 page table code,
> + * we must always honor the following condition:
> + *
> + * Number of levels in Stage1 >= Number of levels in Stage2.
> + *
> + * So clamp the ipa limit further down to limit the number of levels.
> + * Since we can concatenate upto 16 tables at entry level, we could
> + * go upto 4bits above the maximum VA addressible with the current
> + * number of levels.
> + */
> + va_max = PGDIR_SHIFT + PAGE_SHIFT - 3;
> + va_max += 4;
> +
> + if (va_max < ipa_max) {
> + kvm_info("Limiting IPA limit to %dbytes due to host VA bits limitation\n",
> + va_max);
> + ipa_max = va_max;
> + }
> +
> + return ipa_max;
> }
>
> static inline void kvm_config_stage2(struct kvm *kvm, u32 ipa_shift)
>

Otherwise looks good.

M.
--
Jazz is not dead. It just smells funny...

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