Hi Suzuki, On Wed, Jul 18, 2018 at 10:19:03AM +0100, 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 > 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). > > Cc: Marc Zyngier <marc.zyngier@xxxxxxx> > Cc: Christoffer Dall <cdall@xxxxxxxxxx> > Cc: Peter Maydel <peter.maydell@xxxxxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx> > --- > All, > > This is not the final API. We are still evaluating the possible > options to create a VM and then configure the VM before any > resources can be allocated (e.g, devices, vCPUs or memory). > See [0] for discussion: > > [0] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-July/587839.html FWIW, I think encoding the size in the type isn't that bad, as it seems in the worst case we'll occupy 24 bits out of the 64-bit type argument at the time being (IPA+SVE), and that's several years into KVM/ARM's life time. I'm sure we'll need a more sophisticated API some day, when we absolutely cannot easily use what we already have, but we can add that API at the time. > --- > Documentation/virtual/kvm/api.txt | 4 ++++ > arch/arm64/include/asm/stage2_pgtable.h | 20 -------------------- > arch/arm64/kvm/guest.c | 3 --- > include/uapi/linux/kvm.h | 9 +++++++++ > virt/kvm/arm/arm.c | 16 ++++++++++++---- > 5 files changed, 25 insertions(+), 27 deletions(-) > > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt > index d10944e..4e76e81 100644 > --- a/Documentation/virtual/kvm/api.txt > +++ b/Documentation/virtual/kvm/api.txt > @@ -122,6 +122,10 @@ 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. > > +On arm64, bits[7-0] of the machine type has been reserved for specifying > +the maximum physical address size for the VM. For backward compatibility, > +value 0 implies the default limit of 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 6743b76..fbdfed7 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/guest.c b/arch/arm64/kvm/guest.c > index 142e610..66fb20c 100644 > --- a/arch/arm64/kvm/guest.c > +++ b/arch/arm64/kvm/guest.c > @@ -475,9 +475,6 @@ int kvm_arm_config_vm(struct kvm *kvm, u32 ipa_shift) > u64 parange; > u8 lvls = stage2_pgtable_levels(ipa_shift); > > - if (ipa_shift != KVM_PHYS_SHIFT) > - return -EINVAL; > - > /* > * Use a minimum 2 level page table to prevent splitting > * host PMD huge pages at stage2. > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 9a40d82..625a11e 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -751,6 +751,15 @@ struct kvm_ppc_resize_hpt { > #define KVM_S390_SIE_PAGE_OFFSET 1 > > /* > + * On arm/arm64, machine type cane be used to request the physical nit: s/cane/can/ > + * address size for the VM. Bits[7-0] has been reserved for the PA > + * 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 0xff > +#define KVM_VM_TYPE_ARM_PHYS_SHIFT(x) \ > + ((x) & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK) > +/* > * ioctls for /dev/kvm fds: > */ > #define KVM_GET_API_VERSION _IO(KVMIO, 0x00) > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c > index 220d886..a96205e 100644 > --- a/virt/kvm/arm/arm.c > +++ b/virt/kvm/arm/arm.c > @@ -111,6 +111,17 @@ void kvm_arch_check_processor_compat(void *rtn) > *(int *)rtn = 0; > } > > +static int kvm_arch_config_vm(struct kvm *kvm, unsigned long type) > +{ > + u32 ipa_shift = KVM_VM_TYPE_ARM_PHYS_SHIFT(type); > + > + if (!ipa_shift) > + ipa_shift = KVM_PHYS_SHIFT; > + if (ipa_shift > kvm_ipa_limit) > + return -E2BIG; > + return kvm_arm_config_vm(kvm, ipa_shift); > +} > + > /** > * kvm_arch_init_vm - initializes a VM data structure > * @kvm: pointer to the KVM struct > @@ -119,10 +130,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) > { > int ret, cpu; > > - if (type) > - return -EINVAL; > - > - ret = kvm_arm_config_vm(kvm, KVM_PHYS_SHIFT); > + ret = kvm_arch_config_vm(kvm, type); > if (ret) > return ret; > > -- > 2.7.4 > Thanks, Christoffer
