Re: [PULL 15/22] x86: Grant AMX permission for guest

[Maxim Levitsky]

On Wed, 2022-03-16 at 17:50 +0000, Daniel P. Berrangé wrote:
> On Wed, Mar 16, 2022 at 05:48:04PM +0000, David Edmondson wrote:
> > On Wednesday, 2022-03-16 at 16:05:01 GMT, Daniel P. Berrangé wrote:
> > 
> > > On Wed, Mar 16, 2022 at 04:57:39PM +0100, Peter Krempa wrote:
> > > > On Tue, Mar 08, 2022 at 12:34:38 +0100, Paolo Bonzini wrote:
> > > > > From: Yang Zhong <yang.zhong@intel.com>
> > > > > 
> > > > > Kernel allocates 4K xstate buffer by default. For XSAVE features
> > > > > which require large state component (e.g. AMX), Linux kernel
> > > > > dynamically expands the xstate buffer only after the process has
> > > > > acquired the necessary permissions. Those are called dynamically-
> > > > > enabled XSAVE features (or dynamic xfeatures).
> > > > > 
> > > > > There are separate permissions for native tasks and guests.
> > > > > 
> > > > > Qemu should request the guest permissions for dynamic xfeatures
> > > > > which will be exposed to the guest. This only needs to be done
> > > > > once before the first vcpu is created.
> > > > > 
> > > > > KVM implemented one new ARCH_GET_XCOMP_SUPP system attribute API to
> > > > > get host side supported_xcr0 and Qemu can decide if it can request
> > > > > dynamically enabled XSAVE features permission.
> > > > > https://lore.kernel.org/all/20220126152210.3044876-1-pbonzini@redhat.com/
> > > > > 
> > > > > Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> > > > > Signed-off-by: Yang Zhong <yang.zhong@intel.com>
> > > > > Signed-off-by: Jing Liu <jing2.liu@intel.com>
> > > > > Message-Id: <20220217060434.52460-4-yang.zhong@intel.com>
> > > > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > > > > ---
> > > > >  target/i386/cpu.c          |  7 +++++
> > > > >  target/i386/cpu.h          |  4 +++
> > > > >  target/i386/kvm/kvm-cpu.c  | 12 ++++----
> > > > >  target/i386/kvm/kvm.c      | 57 
> > > > > ++++++++++++++++++++++++++++++++++++++
> > > > >  target/i386/kvm/kvm_i386.h |  1 +
> > > > >  5 files changed, 75 insertions(+), 6 deletions(-)
> > > > 
> > > > With this commit qemu crashes for me when invoking the following
> > > > QMP command:
> > > 
> > > It is way worse than that even. If you remove '-S' you get an
> > > immediate kaboom on startup on AMD hosts
> > 
> > Which AMD CPU is in this host?
> 
> AMD EPYC 7302P
> 
> 
> With regards,
> Daniel

my 3970X - same issue.

Best regards,
        Maxim Levitsky