Re: [RFC PATCH v2 16/22] i386/xen: handle VCPUOP_register_vcpu_info

[Paul Durrant]

On 13/12/2022 00:13, David Woodhouse wrote:
> On Mon, 2022-12-12 at 14:58 +0000, Paul Durrant wrote:
> > On 09/12/2022 09:56, David Woodhouse wrote:
> > > From: Joao Martins <
> > > joao.m.martins@oracle.com
> > > >
> > >
> > > Handle the hypercall to set a per vcpu info, and also wire up the
> > > default
> > > vcpu_info in the shared_info page for the first 32 vCPUs.
> > >
> > > To avoid deadlock within KVM a vCPU thread must set its *own*
> > > vcpu_info
> > > rather than it being set from the context in which the hypercall is
> > > invoked.
> > >
> > > Add the vcpu_info (and default) GPA to the vmstate_x86_cpu for
> > > migration,
> > > and restore it in kvm_arch_put_registers() appropriately.
> > >
> > > Signed-off-by: Joao Martins <
> > > joao.m.martins@oracle.com
> > > >
> > > Signed-off-by: David Woodhouse <
> > > dwmw@amazon.co.uk
> > > >
> > > ---
> > >    target/i386/cpu.h        |  2 ++
> > >    target/i386/kvm/kvm.c    | 19 +++++++++++
> > >    target/i386/machine.c    | 21 ++++++++++++
> > >    target/i386/trace-events |  1 +
> > >    target/i386/xen.c        | 74
> > > +++++++++++++++++++++++++++++++++++++---
> > >    target/i386/xen.h        |  1 +
> > >    6 files changed, 113 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > > index c6c57baed5..109b2e5669 100644
> > > --- a/target/i386/cpu.h
> > > +++ b/target/i386/cpu.h
> > > @@ -1788,6 +1788,8 @@ typedef struct CPUArchState {
> > >    #endif
> > >    #if defined(CONFIG_KVM)
> > >        struct kvm_nested_state *nested_state;
> > > +    uint64_t xen_vcpu_info_gpa;
> > > +    uint64_t xen_vcpu_info_default_gpa;
> > >    #endif
> > >    #if defined(CONFIG_HVF)
> > >        HVFX86LazyFlags hvf_lflags;
> > > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> > > index ebde6bc204..fa45e2f99a 100644
> > > --- a/target/i386/kvm/kvm.c
> > > +++ b/target/i386/kvm/kvm.c
> > > @@ -1811,6 +1811,9 @@ int kvm_arch_init_vcpu(CPUState *cs)
> > >            has_msr_hv_hypercall = true;
> > >        }
> > >    
> > > +    env->xen_vcpu_info_gpa = UINT64_MAX;
> > > +    env->xen_vcpu_info_default_gpa = UINT64_MAX;
> >
> >
> > There was an INVALID_GPA definition for shared info. Looks like we
> > could use it here too.
>
> There was, and I started trying to use it, but it fell foul of the "is
> this going to live in target/ or hw/ and who can include what from
> where?" and I decided to just use UINT64_MAX for now and keep typing.
>
> That will work out in the end, I'm sure.

Hopefully 
https://lore.kernel.org/lkml/20221209023622.274715-1-yu.c.zhang@linux.intel.com/ 
will help.

> > Some sanity checks wouldn't go a miss here...
> >
> > rvi.offset should:
> > a) be < TARGET_PAGE_SIZE, and
> > b) ba aligned to vcpu_info_t size
>
> Ack.