Messages in this thread | | | From | Juergen Gross <> | Subject | Re: [PATCH v3 3/4] x86/kvm: add max number of vcpus for hyperv emulation | Date | Thu, 18 Nov 2021 08:43:31 +0100 |
| |
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@suse.com> >> --- >> 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 1024U > > I 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 [unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature] | |