Re: [PATCH V11 10/10] arm/arm64: KVM: add guest SEA support

[Baicar, Tyler]

Hello James,


On 3/6/2017 3:28 AM, James Morse wrote:
> On 28/02/17 19:43, Baicar, Tyler wrote:
> > On 2/24/2017 3:42 AM, James Morse wrote:
> > > On 21/02/17 21:22, Tyler Baicar wrote:
> > > > Currently external aborts are unsupported by the guest abort
> > > > handling. Add handling for SEAs so that the host kernel reports
> > > > SEAs which occur in the guest kernel.
> > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > > index b2d57fc..403277b 100644
> > > > --- a/arch/arm64/mm/fault.c
> > > > +++ b/arch/arm64/mm/fault.c
> > > > @@ -602,6 +602,24 @@ static const char *fault_name(unsigned int esr)
> > > >    }
> > > >
> > > >    /*
> > > > + * Handle Synchronous External Aborts that occur in a guest kernel.
> > > > + */
> > > > +int handle_guest_sea(unsigned long addr, unsigned int esr)
> > > > +{
> > > > +    if(IS_ENABLED(HAVE_ACPI_APEI_SEA)) {
> > > > +        nmi_enter();
> > > > +        ghes_notify_sea();
> > > > +        nmi_exit();
> > > This nmi stuff was needed for synchronous aborts that may have interrupted
> > > APEI's interrupts-masked code. We want to avoid trying to take the same set of
> > > locks, hence taking the in_nmi() path through APEI. Here we know we interrupted
> > > a guest, so there is no risk that we have interrupted APEI on the host.
> > > ghes_notify_sea() can safely take the normal path.
> > Makes sense, I can remove the nmi_* calls here.
> Just occurs to me: if we do this we need to add the rcu_read_lock() in
> ghes_notify_sea() as its not protected by the rcu/nmi weirdness.
True, would you suggest leaving these nmi_* calls or adding the rcu_* 
calls? And since that's only needed for this KVM case, shouldn't the 
rcu_* calls just replace the nmi_* calls here (outside of ghes_notify_sea)?

Thanks,
Tyler

--
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.