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Message-ID: <d915accb-966f-5c3d-f969-45512ebd8ca5@redhat.com>
Date: Tue, 25 Sep 2018 11:59:31 +0200
From: Auger Eric <eric.auger@...hat.com>
To: Suzuki K Poulose <suzuki.poulose@....com>,
linux-arm-kernel@...ts.infradead.org
Cc: kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
marc.zyngier@....com, cdall@...nel.org, pbonzini@...hat.com,
rkrcmar@...hat.com, will.deacon@....com, catalin.marinas@....com,
james.morse@....com, dave.martin@....com, julien.grall@....com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 16/18] kvm: arm64: Set a limit on the IPA size
Hi Suzuki,
On 9/17/18 12:41 PM, 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, we can allow VMs to have
> larger IPA. This patch introduces a the maximum IPA size
> supported on the host.
to be reworded
This is decided by the following factors :
>
> 1) Maximum PARange supported by the CPUs - This can be inferred
> from the system wide safe value.
> 2) Maximum PA size supported by the host kernel (48 vs 52)
> 3) Number of levels in the host page table (as we base our
> stage2 tables on the host table helpers).
>
> 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.
>
> Host configuration | Unsupported IPA ranges
> 39bit VA, 4K | [44, 48]
> 36bit VA, 16K | [41, 48]
> 42bit VA, 64K | [47, 52]
>
> 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@....com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Christoffer Dall <cdall@...nel.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....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/arm/include/asm/kvm_mmu.h | 2 ++
> arch/arm64/include/asm/kvm_host.h | 2 ++
> arch/arm64/kvm/reset.c | 43 +++++++++++++++++++++++++++++++
> virt/kvm/arm/arm.c | 2 ++
> 4 files changed, 49 insertions(+)
>
> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> index 12ae5fbbcf01..5ad1a54f98dc 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -358,6 +358,8 @@ static inline int hyp_map_aux_data(void)
>
> #define kvm_phys_to_vttbr(addr) (addr)
>
> +static inline void kvm_set_ipa_limit(void) {}
> +
> #endif /* !__ASSEMBLY__ */
>
> #endif /* __ARM_KVM_MMU_H__ */
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 5ecd457bce7d..f0474061851d 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -513,6 +513,8 @@ static inline int kvm_arm_have_ssbd(void)
> void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu);
> void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu);
>
> +void kvm_set_ipa_limit(void);
> +
> #define __KVM_HAVE_ARCH_VM_ALLOC
> struct kvm *kvm_arch_alloc_vm(void);
> void kvm_arch_free_vm(struct kvm *kvm);
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 51ecf0f7c912..76972b19bdd7 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -34,6 +34,9 @@
> #include <asm/kvm_coproc.h>
> #include <asm/kvm_mmu.h>
>
> +/* Maximum phys_shift supported for any VM on this host */
> +static u32 kvm_ipa_limit;
> +
> /*
> * ARMv8 Reset Values
> */
> @@ -135,6 +138,46 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> return kvm_timer_vcpu_reset(vcpu);
> }
>
> +void kvm_set_ipa_limit(void)
> +{
> + 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;
I don't really get what does happen in this case. The CPU cannot handle
PA up to ipa_max so can the VM run properly? In case it is a
showstopper, kvm_set_ipa_limit should return an error, cascaded by
init_common_resources. Otherwise the warning message may be reworded.
> + }
> +
> + /* 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
addressable?
> + * 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;
you have a trace for this limitation but none for the comparison against
PHYS_MASK_SHIFT.
> + }
> +
> + kvm_ipa_limit = ipa_max;
> +}
> +
> /*
> * Configure the VTCR_EL2 for this VM. The VTCR value is common
> * across all the physical CPUs on the system. We use system wide
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 43e716bc3f08..631f9a3ad99a 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -1413,6 +1413,8 @@ static int init_common_resources(void)
> kvm_vmid_bits = kvm_get_vmid_bits();
> kvm_info("%d-bit VMID\n", kvm_vmid_bits);
>
> + kvm_set_ipa_limit();
As we have a kvm_info for the supported vmid_bits, may be good to output
the max IPA size supported by the host whatever the applied clamps?
Thanks
Eric
> +
> return 0;
> }
>
>
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