Hi, On 4/27/20 6:33 PM, Marc Zyngier wrote: > On Mon, 27 Apr 2020 16:00:58 +0100 > Alexandru Elisei <[email protected]> wrote: > >> Hi, >> >> On 4/27/20 3:44 PM, Alexandru Elisei wrote: >>> Hi, >>> >>> On 4/27/20 3:17 PM, Marc Zyngier wrote: >>>> On arm64, the maximum number of vcpus is constrained by the type >>>> of interrupt controller that has been selected (GICv2 imposes a >>>> limit of 8 vcpus, while GICv3 currently has a limit of 512). >>>> >>>> It is thus important to request this limit on the VM file descriptor >>>> rather than on the one that corresponds to /dev/kvm, as the latter >>>> is likely to return something that doesn't take the constraints into >>>> account. >>>> >>>> Reported-by: Ard Biesheuvel <[email protected]> >>>> Signed-off-by: Marc Zyngier <[email protected]> >>>> --- >>>> kvm.c | 4 ++-- >>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/kvm.c b/kvm.c >>>> index e327541..3d5173d 100644 >>>> --- a/kvm.c >>>> +++ b/kvm.c >>>> @@ -406,7 +406,7 @@ int kvm__recommended_cpus(struct kvm *kvm) >>>> { >>>> int ret; >>>> >>>> - ret = ioctl(kvm->sys_fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS); >>>> + ret = ioctl(kvm->vm_fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS); >>>> if (ret <= 0) >>>> /* >>>> * api.txt states that if KVM_CAP_NR_VCPUS does not exist, >>>> @@ -421,7 +421,7 @@ int kvm__max_cpus(struct kvm *kvm) >>>> { >>>> int ret; >>>> >>>> - ret = ioctl(kvm->sys_fd, KVM_CHECK_EXTENSION, KVM_CAP_MAX_VCPUS); >>>> + ret = ioctl(kvm->vm_fd, KVM_CHECK_EXTENSION, KVM_CAP_MAX_VCPUS); >>>> if (ret <= 0) >>>> ret = kvm__recommended_cpus(kvm); >>>> >>> I've checked that gic__create comes before the call kvm__recommended_capus: >>> gic__create is in core_init (called via kvm__init->kvm_arch_init), and >>> kvm__recommended_cpus is in base_init (called via kvm__cpu_init -> >>> kvm__{recommended,max}_cpus). >>> >>> The KVM api documentation states that KVM_CHECK_EXTENSION is available for >>> the vm >>> fd only if the system capability KVM_CAP_CHECK_EXTENSION_VM is present. >>> kvmtool >>> already has a function for checking extensions on the vm fd, it's called >>> kvm__supports_vm_extension. Can we use that instead of doing the ioctl >>> directly on >>> the vm fd? >> Scratch that, kvm__supports_vm_extension returns a bool, not an int. >> How about we write kvm__check_vm_extension that returns an int, and >> kvm__supports_vm_extension calls it? > That, or we just change the return type for kvm__supports_vm_extension, > and hack the only places that uses it so far (the GIC code) to detect > the error.
Yep, whatever you prefer. Thanks, Alex _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
