Re: [PATCH v2 13/17] kvm: arm/arm64: Allow tuning the physical address size for VM

From: Suzuki K Poulose
Date: Wed Apr 25 2018 - 12:22:50 EST

On 25/04/18 17:10, Julien Grall wrote:
Hi Suzuki,

On 27/03/18 14:15, Suzuki K Poulose wrote:
Allow specifying the physical address size for a new VM via
the kvm_type argument for KVM_CREATE_VM ioctl. This allows
us to finalise the stage2 page table format as early as possible
and hence perform the right checks on the memory slots without
complication. The size is encoded as Log2(PA_Siz) in the bits[7:0]


--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -740,6 +740,16 @@ struct kvm_ppc_resize_hpt {
 #define KVM_S390_SIE_PAGE_OFFSET 1
+ * On arm/arm64, machine type can be used to request the physical
+ * address size for the VM. Bits [7-0] have been reserved for the
+ * PA size shift (i.e, log2(PA-Size)). For backward compatibility,

I would s/PA-Size/PA_Size/ to avoid the impression that it is a substraction.


+ * value 0 implies the default IPA size, which is 40bits.
+ */
ÂÂ * ioctls for /dev/kvm fds:
ÂÂ */
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 53bb05c..13eb66f 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -110,6 +110,25 @@ void kvm_arch_check_processor_compat(void *rtn)
+static int kvm_arch_config_vm(struct kvm *kvm, unsigned long type)
+ÂÂÂ u32 ipa_shift = (u32)type & KVM_VM_TYPE_ARM_PHYS_SHIFT_MASK;

How about using KVM_VM_TYPE_ARM_PHYS_SHIFT(type) directly here?

Thanks for that, I have this already fixed in for v3.

ÂÂ * kvm_arch_init_vm - initializes a VM data structure
ÂÂ * @kvm:ÂÂÂ pointer to the KVM struct
@@ -118,8 +137,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
ÂÂÂÂÂ int ret, cpu;
-ÂÂÂ if (type)
+ÂÂÂ ret = kvm_arch_config_vm(kvm, type);
+ÂÂÂ if (ret)
+ÂÂÂÂÂÂÂ return ret;
ÂÂÂÂÂ kvm->arch.last_vcpu_ran = alloc_percpu(typeof(*kvm->arch.last_vcpu_ran));
ÂÂÂÂÂ if (!kvm->arch.last_vcpu_ran)


Thanks for the review.