Hi Marc,
On 3/11/21 11:00 AM, Marc Zyngier wrote:
KVM/arm64 has forever used a 40bit default IPA space, partially due to its 32bit heritage (where the only choice is 40bit).
However, there are implementations in the wild that have a *cough* much smaller *cough* IPA space, which leads to a misprogramming of VTCR_EL2, and a guest that is stuck on its first memory access if userspace dares to ask for the default IPA setting (which most VMMs do).
Instead, blundly reject the creation of such VM, as we can't satisfy the requirements from userspace (with a one-off warning). Also clarify the boot warning, and document that the VM creation will fail when an unsupported IPA size is probided.
Although this is an ABI change, it doesn't really change much for userspace:
the guest couldn't run before this change, but no error was returned. At least userspace knows what is happening.
a memory slot that was accepted because it did fit the default IPA space now doesn't even get a chance to be registered.
The other thing that is left doing is to convince userspace to actually use the IPA space setting instead of relying on the antiquated default.
Fixes: 233a7cb23531 ("kvm: arm64: Allow tuning the physical address size for VM") Signed-off-by: Marc Zyngier maz@kernel.org Cc: stable@vger.kernel.org
Reviewed-by: Eric Auger eric.auger@redhat.com
Thanks
Eric
Documentation/virt/kvm/api.rst | 3 +++ arch/arm64/kvm/reset.c | 12 ++++++++---- 2 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 1a2b5210cdbf..38e327d4b479 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -182,6 +182,9 @@ is dependent on the CPU capability and the kernel configuration. The limit can be retrieved using KVM_CAP_ARM_VM_IPA_SIZE of the KVM_CHECK_EXTENSION ioctl() at run-time. +Creation of the VM will fail if the requested IPA size (whether it is +implicit or explicit) is unsupported on the host.
Please note that configuring the IPA size does not affect the capability exposed by the guest CPUs in ID_AA64MMFR0_EL1[PARange]. It only affects size of the address translated by the stage2 level (guest physical to diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c index 47f3f035f3ea..9d3d09a89894 100644 --- a/arch/arm64/kvm/reset.c +++ b/arch/arm64/kvm/reset.c @@ -324,10 +324,9 @@ int kvm_set_ipa_limit(void) } kvm_ipa_limit = id_aa64mmfr0_parange_to_phys_shift(parange);
- WARN(kvm_ipa_limit < KVM_PHYS_SHIFT,
"KVM IPA Size Limit (%d bits) is smaller than default size\n",kvm_ipa_limit);- kvm_info("IPA Size Limit: %d bits\n", kvm_ipa_limit);
- kvm_info("IPA Size Limit: %d bits%s\n", kvm_ipa_limit,
((kvm_ipa_limit < KVM_PHYS_SHIFT) ?" (Reduced IPA size, limited VM/VMM compatibility)" : ""));return 0; } @@ -356,6 +355,11 @@ int kvm_arm_setup_stage2(struct kvm *kvm, unsigned long type) return -EINVAL; } else { phys_shift = KVM_PHYS_SHIFT;
if (phys_shift > kvm_ipa_limit) {pr_warn_once("%s using unsupported default IPA limit, upgrade your VMM\n",current->comm);return -EINVAL;}mmfr0 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1);