On 09/16 09:33, Dr. David Alan Gilbert wrote: > * Wei Huang (wei.huang2@xxxxxxx) wrote: > > On 09/15 05:51, Dr. David Alan Gilbert wrote: > > > * Vitaly Kuznetsov (vkuznets@xxxxxxxxxx) wrote: > > > > With QEMU and newer AMD CPUs (namely: Epyc 'Rome') the current limit for > > > > Could you elaborate on this limit? On Rome, I counted ~35 CPUID functions which > > include Fn0000_xxxx, Fn4000_xxxx and Fn8000_xxxx. > > On my 7302P the output of: > cpuid -1 -r | wc -l > > is 61, there is one line of header in there. > > However in a guest I see more; and I think that's because KVM tends to > list the CPUID entries for a lot of disabled Intel features, even on > AMD, e.g. 0x11-0x1f which AMD doesn't have, are listed in a KVM guest. > Then you add the KVM CPUIDs at 4...0 and 4....1. > It is indeed a mixing bag. Some are added even though AMD CPU doesn't define them. BTW I also believe that cpuid command lists more CPUIDs than the real value of cpuid->nent in kvm_vcpu_ioctl_set_cpuid(2). Anyway I don't have objection to this patchset. > IMHO we should be filtering those out for at least two reasons: > a) They're wrong > b) We're probably not keeping the set of visible CPUID fields the same > when we move between host kernels, and that can't be good for > migration. > > Still, those are separate problems. > > Dave > > > > > KVM_MAX_CPUID_ENTRIES(80) is reported to be hit. Last time it was raised > > > > from '40' in 2010. We can, of course, just bump it a little bit to fix > > > > the immediate issue but the report made me wonder why we need to pre- > > > > allocate vcpu->arch.cpuid_entries array instead of sizing it dynamically. > > > > This RFC is intended to feed my curiosity. > > > > > > > > Very mildly tested with selftests/kvm-unit-tests and nothing seems to > > > > break. I also don't have access to the system where the original issue > > > > was reported but chances we're fixing it are very good IMO as just the > > > > second patch alone was reported to be sufficient. > > > > > > > > Reported-by: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx> > > > > > > Oh nice, I was just going to bump the magic number :-) > > > > > > Anyway, this seems to work for me, so: > > > > > > Tested-by: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx> > > > > > > > I tested on two platforms and the patches worked fine. So no objection on the > > design. > > > > Tested-by: Wei Huang <wei.huang2@xxxxxxx> > > > > > > Vitaly Kuznetsov (2): > > > > KVM: x86: allocate vcpu->arch.cpuid_entries dynamically > > > > KVM: x86: bump KVM_MAX_CPUID_ENTRIES > > > > > > > > arch/x86/include/asm/kvm_host.h | 4 +-- > > > > arch/x86/kvm/cpuid.c | 55 ++++++++++++++++++++++++--------- > > > > arch/x86/kvm/x86.c | 1 + > > > > 3 files changed, 43 insertions(+), 17 deletions(-) > > > > > > > > -- > > > > 2.25.4 > > > > > > > -- > > > Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK > > > > > > -- > Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK >
