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Date: Tue, 25 Sep 2018 12:00:21 +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,
Peter Maydel <peter.maydell@...aro.org>
Subject: Re: [PATCH v5 18/18] kvm: arm64: Allow tuning the physical address
size for VM
Hi Suzuki,
On 9/17/18 12:41 PM, Suzuki K Poulose wrote:
> Allow specifying the physical address size limit for a new
> VM via the kvm_type argument for the KVM_CREATE_VM ioctl. This
> allows us to finalise the stage2 page table as early as possible
> and hence perform the right checks on the memory slots
> without complication. The size is ecnoded as Log2(PA_Size) in
encoded
> bits[7:0] of the type field. For backward compatibility the
> value 0 is reserved and implies 40bits. Also, lift the limit
> of the IPA to host limit and allow lower IPA sizes (e.g, 32).
>
> The userspace could check the extension KVM_CAP_ARM_VM_PHYS_SHIFT
> for the availability of this feature. The cap check returns the
> maximum limit for the physical address shift supported by the host.
>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Christoffer Dall <cdall@...nel.org>
> Cc: Peter Maydel <peter.maydell@...aro.org>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
> Changes since v4:
> - Fold the introduction of the KVM_CAP_ARM_VM_PHYS_SHIFT to this
> patch to allow detection of the availability of the feature for
> userspace.
> - Document the API
> - Restrict the feature only to arm64.
> Changes since V3:
> - Switch to a CAP, that can be checkd via EXTENSIONS on KVM device
> fd, rather than a dedicated ioctl.
> ---
> Documentation/virtual/kvm/api.txt | 8 ++++++++
> arch/arm64/include/asm/stage2_pgtable.h | 20 --------------------
> arch/arm64/kvm/reset.c | 20 ++++++++++++++++----
> include/uapi/linux/kvm.h | 10 ++++++++++
> 4 files changed, 34 insertions(+), 24 deletions(-)
>
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index c664064f76fb..f860251ff27c 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -122,6 +122,14 @@ the default trap & emulate implementation (which changes the virtual
> memory layout to fit in user mode), check KVM_CAP_MIPS_VZ and use the
> flag KVM_VM_MIPS_VZ.
>
> +To configure the physical address space size for a VM (IPA size) on arm64,
> +check KVM_CAP_ARM_VM_PHYS_SHIFT (which returns the maximum limit for the
> +IPA shift) and use KVM_VM_TYPE_ARM_PHYS_SHIFT(PHYS_SHIFT). Bits[7-0] of the
> +machine type has been reserved for specifying the PHYS_SHIFT.
are reserved to pass the PHYS_SHIFT?
> +The supported range is [32...IPA_LIMIT], where IPA_LIMIT could be
s/could be/is
> +identified by checking KVM_CAP_ARM_VM_PHYS_SHIFT. For backward compatibility
> +a value of 0 selects 40bits.
> +
>
> 4.3 KVM_GET_MSR_INDEX_LIST, KVM_GET_MSR_FEATURE_INDEX_LIST
>
> diff --git a/arch/arm64/include/asm/stage2_pgtable.h b/arch/arm64/include/asm/stage2_pgtable.h
> index 6a56fdff0823..0b339f5a4a7c 100644
> --- a/arch/arm64/include/asm/stage2_pgtable.h
> +++ b/arch/arm64/include/asm/stage2_pgtable.h
> @@ -42,28 +42,8 @@
> * the range (IPA_SHIFT, IPA_SHIFT - 4).
> */
> #define stage2_pgtable_levels(ipa) ARM64_HW_PGTABLE_LEVELS((ipa) - 4)
> -#define STAGE2_PGTABLE_LEVELS stage2_pgtable_levels(KVM_PHYS_SHIFT)
> #define kvm_stage2_levels(kvm) VTCR_EL2_LVLS(kvm->arch.vtcr)
>
> -/*
> - * With all the supported VA_BITs and 40bit guest IPA, the following condition
> - * is always true:
> - *
> - * STAGE2_PGTABLE_LEVELS <= CONFIG_PGTABLE_LEVELS
> - *
> - * We base our stage-2 page table walker helpers on this assumption and
> - * fall back to using the host version of the helper wherever possible.
> - * i.e, if a particular level is not folded (e.g, PUD) at stage2, we fall back
> - * to using the host version, since it is guaranteed it is not folded at host.
> - *
> - * If the condition breaks in the future, we can rearrange the host level
> - * definitions and reuse them for stage2. Till then...
> - */
> -#if STAGE2_PGTABLE_LEVELS > CONFIG_PGTABLE_LEVELS
> -#error "Unsupported combination of guest IPA and host VA_BITS."
> -#endif
> -
> -
> /* stage2_pgdir_shift() is the size mapped by top-level stage2 entry for the VM */
> #define stage2_pgdir_shift(kvm) pt_levels_pgdir_shift(kvm_stage2_levels(kvm))
> #define stage2_pgdir_size(kvm) (1ULL << stage2_pgdir_shift(kvm))
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 0393bb974b23..c9640159e11f 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -89,6 +89,9 @@ int kvm_arch_dev_ioctl_check_extension(struct kvm *kvm, long ext)
> case KVM_CAP_VCPU_EVENTS:
> r = 1;
> break;
> + case KVM_CAP_ARM_VM_PHYS_SHIFT:
> + r = kvm_ipa_limit;
> + break;
> default:
> r = 0;
> }
> @@ -190,16 +193,25 @@ int kvm_arm_config_vm(struct kvm *kvm, unsigned long type)
> {
> u64 vtcr = VTCR_EL2_FLAGS;
> u64 parange;
> - u8 lvls;
> + u8 lvls, ipa_shift;
>
> - if (type)
> + if (type & ~KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK)
> return -EINVAL;
>
> + ipa_shift = KVM_VM_TYPE_ARM_PHYS_SHIFT(type);
> + if (ipa_shift) {
> + if (ipa_shift > kvm_ipa_limit ||
> + ipa_shift < 32)
> + return -EINVAL;
> + } else {
> + ipa_shift = KVM_PHYS_SHIFT;
> + }
> +
> /*
> * Use a minimum 2 level page table to prevent splitting
> * host PMD huge pages at stage2.
> */
> - lvls = stage2_pgtable_levels(KVM_PHYS_SHIFT);
> + lvls = stage2_pgtable_levels(ipa_shift);
> if (lvls < 2)
> lvls = 2;
>
> @@ -221,7 +233,7 @@ int kvm_arm_config_vm(struct kvm *kvm, unsigned long type)
> VTCR_EL2_VS_8BIT;
>
> vtcr |= VTCR_EL2_LVLS_TO_SL0(lvls);
> - vtcr |= VTCR_EL2_T0SZ(KVM_PHYS_SHIFT);
> + vtcr |= VTCR_EL2_T0SZ(ipa_shift);
>
> kvm->arch.vtcr = vtcr;
> return 0;
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 07548de5c988..2a6b29c446db 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -750,6 +750,15 @@ struct kvm_ppc_resize_hpt {
>
> #define KVM_S390_SIE_PAGE_OFFSET 1
>
> +/*
> + * On arm64, machine type can be used to request the physical
> + * address size for the VM. Bits[7-0] has been reserved for the PA
s/has been reserved/are?
Thanks
Eric
> + * size shift (i.e, log2(PA_Size)). For backward compatibility,
> + * value 0 implies the default IPA size, 40bits.
> + */
> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK 0xffULL
> +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \
> + ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK)
> /*
> * ioctls for /dev/kvm fds:
> */
> @@ -952,6 +961,7 @@ struct kvm_ppc_resize_hpt {
> #define KVM_CAP_S390_HPAGE_1M 156
> #define KVM_CAP_NESTED_STATE 157
> #define KVM_CAP_ARM_INJECT_SERROR_ESR 158
> +#define KVM_CAP_ARM_VM_PHYS_SHIFT 159 /* returns maximum PA shift for a VM */
>
> #ifdef KVM_CAP_IRQ_ROUTING
>
>
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