On 17.11.21 21:50, Sean Christopherson wrote:
On Tue, Nov 16, 2021, Juergen Gross wrote:When emulating Hyperv the theoretical maximum of vcpus supported is 4096, as this is the architectural limit for sending IPIs via the PV interface. For restricting the actual supported number of vcpus for that case introduce another define KVM_MAX_HYPERV_VCPUS and set it to 1024, like today's KVM_MAX_VCPUS. Make both values unsigned ones as this will be needed later. The actual number of supported vcpus for Hyperv emulation will be the lower value of both defines. This is a preparation for a future boot parameter support of the max number of vcpus for a KVM guest. Signed-off-by: Juergen Gross <jgross@xxxxxxxx> --- V3: - new patch --- arch/x86/include/asm/kvm_host.h | 3 ++- arch/x86/kvm/hyperv.c | 15 ++++++++------- 2 files changed, 10 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 886930ec8264..8ea03ff01c45 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -38,7 +38,8 @@#define __KVM_HAVE_ARCH_VCPU_DEBUGFS -#define KVM_MAX_VCPUS 1024+#define KVM_MAX_VCPUS 1024U +#define KVM_MAX_HYPERV_VCPUS 1024UI don't see any reason to put this in kvm_host.h, it should never be used outside of hyperv.c.
Okay, fine with me.
#define KVM_MAX_VCPU_IDS kvm_max_vcpu_ids() /* memory slots that are not exposed to userspace */ #define KVM_PRIVATE_MEM_SLOTS 3 diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index 4a555f32885a..c0fa837121f1 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -41,7 +41,7 @@ /* "Hv#1" signature */ #define HYPERV_CPUID_SIGNATURE_EAX 0x31237648-#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, 64)+#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_HYPERV_VCPUS, 64)static void stimer_mark_pending(struct kvm_vcpu_hv_stimer *stimer,bool vcpu_kick); @@ -166,7 +166,7 @@ static struct kvm_vcpu *get_vcpu_by_vpidx(struct kvm *kvm, u32 vpidx) struct kvm_vcpu *vcpu = NULL; int i;- if (vpidx >= KVM_MAX_VCPUS)+ if (vpidx >= min(KVM_MAX_VCPUS, KVM_MAX_HYPERV_VCPUS))IMO, this is conceptually wrong. KVM should refuse to allow Hyper-V to be enabled if the max number of vCPUs exceeds what can be supported, or should refuse to create
TBH, I wasn't sure where to put this test. Is there a guaranteed sequence of ioctl()s regarding vcpu creation (or setting the max number of vcpus) and the Hyper-V enabling?
the vCPUs. I agree it makes sense to add a Hyper-V specific limit, since there are Hyper-V structures that have a hard limit, but detection of violations should be a BUILD_BUG_ON, not a silent failure at runtime.
A BUILD_BUG_ON won't be possible with KVM_MAX_VCPUS being selecteble via boot parameter. Juergen
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