Re: [PATCH v3 21/21] KVM: arm64: Don't constrain maximum IPA size based on host configuration

Gavin Shan
2020-09-03T05:11:05Z

Hi Will,

On 8/25/20 7:39 PM, Will Deacon wrote:
> Now that the guest stage-2 page-tables are managed independently from
> the host stage-1 page-tables, we can avoid constraining the IPA size
> based on the host and instead limit it only based on the PARange field
> of the ID_AA64MMFR0 register.
>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Quentin Perret <qperret@google.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
> arch/arm64/kvm/reset.c | 38 +++++---------------------------------
> 1 file changed, 5 insertions(+), 33 deletions(-)
>

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index ee33875c5c2a..471ee9234e40 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -339,7 +339,7 @@ u32 get_kvm_ipa_limit(void)
>
> int kvm_set_ipa_limit(void)
> {
> - unsigned int ipa_max, pa_max, va_max, parange, tgran_2;
> + unsigned int parange, tgran_2;
> u64 mmfr0;
>
> mmfr0 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1);
> @@ -376,38 +376,10 @@ int kvm_set_ipa_limit(void)
> break;
> }
>
> - pa_max = id_aa64mmfr0_parange_to_phys_shift(parange);
> -
> - /* Clamp the IPA limit to the PA size supported by the kernel */
> - ipa_max = (pa_max > PHYS_MASK_SHIFT) ? PHYS_MASK_SHIFT : pa_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 addressable with the current
> - * number of levels.
> - */
> - va_max = PGDIR_SHIFT + PAGE_SHIFT - 3;
> - va_max += 4;
> -
> - if (va_max < ipa_max)
> - ipa_max = va_max;
> -
> - /*
> - * If the final limit is lower than the real physical address
> - * limit of the CPUs, report the reason.
> - */
> - if (ipa_max < pa_max)
> - pr_info("kvm: Limiting the IPA size due to kernel %s Address limit\n",
> - (va_max < pa_max) ? "Virtual" : "Physical");
> -
> - WARN(ipa_max < KVM_PHYS_SHIFT,
> - "KVM IPA limit (%d bit) is smaller than default size\n", ipa_max);
> - kvm_ipa_limit = ipa_max;
> + kvm_ipa_limit = id_aa64mmfr0_parange_to_phys_shift(parange);
> + WARN(kvm_ipa_limit < KVM_PHYS_SHIFT,
> + "KVM IPA limit (%d bit) is smaller than default size\n",
> + kvm_ipa_limit);
> kvm_info("IPA Size Limit: %dbits\n", kvm_ipa_limit);
>
> return 0;
>

Thanks,
Gavin