Re: [PATCH v6 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active

[Brijesh Singh]

On 09/10/2018 08:29 AM, Sean Christopherson wrote:
...

> > > > + */
> > > > +static struct pvclock_vsyscall_time_info
> > > > +			hv_clock_aux[NR_CPUS] __decrypted_aux;
> > > Hmm, so worst case that's 64 4K pages:
> > >
> > > (8192*32)/4096 = 64 4K pages.
> > We can minimize the worst case memory usage. The number of VCPUs
> > supported by KVM maybe less than NR_CPUS. e.g Currently KVM_MAX_VCPUS is
> > set to 288
>
> KVM_MAX_VCPUS is a property of the host, whereas this code runs in the
> guest, e.g.ÂKVM_MAX_VCPUS could be 2048 in the host for all we know.


IIRC, during guest creation time qemu will check the host supported
VCPUS count. If count is greater than KVM_MAX_VCPUS then it will
fail to launch guest (or fail to hot plug vcpus). In other words, the
number of vcpus in a KVM guest will never to > KVM_MAX_VCPUS.

Am I missing something ?