Re: [Qemu-ppc] [PATCH] spapr/xive: Sanity checks of OV5 during CAS

[Greg Kurz]

On Thu, 16 May 2019 12:09:57 +0530
Satheesh Rajendran <address@hidden> wrote:

> On Wed, May 15, 2019 at 07:04:24PM +0200, Greg Kurz wrote:
> > If a machine is started with ic-mode=xive but the guest only knows
> > about XICS, eg. an RHEL 7.6 guest, the kernel panics. This is
> > expected but a bit unfortunate since the crash doesn't provide
> > much information for the end user to guess what's happening.
> > 
> > Detect that during CAS and exit QEMU with a proper error message
> > instead, like it is already done for the MMU.
> > 
> > Even if this is less likely to happen, the opposite case of a guest
> > that only knows about XIVE would certainly fail all the same if the
> > machine is started with ic-mode=xics.
> > 
> > Also, the only valid values a guest can pass in byte 23 of OV5 during
> > CAS are 0b00 (XIVE legacy mode) and 0b01 (XIVE exploitation mode). Any
> > other value is a bug, at least with the current spec. Again, it does
> > not seem right to let the guest go on without a precise idea of the
> > interrupt mode it asked for.
> > 
> > Handle these cases as well.
> > 
> > Reported-by: Satheesh Rajendran <address@hidden>
> > Signed-off-by: Greg Kurz <address@hidden>
> > ---
> >  hw/ppc/spapr_hcall.c |   24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> > 
> > diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> > index 6c16d2b12040..63a55614b83d 100644
> > --- a/hw/ppc/spapr_hcall.c
> > +++ b/hw/ppc/spapr_hcall.c
> > @@ -1513,6 +1513,7 @@ static target_ulong 
> > h_client_architecture_support(PowerPCCPU *cpu,
> >      bool guest_radix;
> >      Error *local_err = NULL;
> >      bool raw_mode_supported = false;
> > +    bool guest_xive;
> > 
> >      cas_pvr = cas_check_pvr(spapr, cpu, &addr, &raw_mode_supported, 
> > &local_err);
> >      if (local_err) {
> > @@ -1545,10 +1546,17 @@ static target_ulong 
> > h_client_architecture_support(PowerPCCPU *cpu,
> >          error_report("guest requested hash and radix MMU, which is 
> > invalid.");
> >          exit(EXIT_FAILURE);
> >      }
> > +    if (spapr_ovec_test(ov5_guest, OV5_XIVE_BOTH)) {
> > +        error_report("guest requested an invalid interrupt mode");
> > +        exit(EXIT_FAILURE);
> > +    }
> > +
> >      /* The radix/hash bit in byte 24 requires special handling: */
> >      guest_radix = spapr_ovec_test(ov5_guest, OV5_MMU_RADIX_300);
> >      spapr_ovec_clear(ov5_guest, OV5_MMU_RADIX_300);
> > 
> > +    guest_xive = spapr_ovec_test(ov5_guest, OV5_XIVE_EXPLOIT);
> > +
> >      /*
> >       * HPT resizing is a bit of a special case, because when enabled
> >       * we assume an HPT guest will support it until it says it
> > @@ -1632,6 +1640,22 @@ static target_ulong 
> > h_client_architecture_support(PowerPCCPU *cpu,
> >                                            ov5_updates) != 0);
> >      }
> > 
> > +    /*
> > +     * Ensure the guest asks for an interrupt mode we support; otherwise
> > +     * terminate the boot.
> > +     */
> > +    if (guest_xive) {
> > +        if (spapr->irq->ov5 == SPAPR_OV5_XIVE_LEGACY) {
> > +            error_report("Guest requested unavailable interrupt mode 
> > (XIVE)");
> > +            exit(EXIT_FAILURE);
> > +        }
> > +    } else {
> > +        if (spapr->irq->ov5 == SPAPR_OV5_XIVE_EXPLOIT) {
> > +            error_report("Guest requested unavailable interrupt mode 
> > (XICS)");  
> 
> Looks like there is a typo in the error msg reported, instead it should be 
> something like below
> 
> "Guest requested unavailable interrupt mode(XIVE), please use supported 
> interrupt mode(ic-type=xics)"
> 

Hmm... Agreed that it may be worth adding some hint for the user to proceed 
but...

> Same for the previous check aswell.
> 
> Coz, I booted 3.10(kernel) guest with ic-type=xive and got a below error, 
> which seems wrong
> 
> 2019-05-16T06:24:58.713261Z qemu-system-ppc64: Guest requested unavailable 
> interrupt mode (XICS)
> 

... this message is ok: the 3.10 kernel based guest _does_ ask for XICS,
which isn't available because of ic-mode=xive.

Cheers,

--
Greg

> Regards,
> -Satheesh.
> 
> > +            exit(EXIT_FAILURE);
> > +        }
> > +    }
> > +
> >      /*
> >       * Generate a machine reset when we have an update of the
> >       * interrupt mode. Only required when the machine supports both
> >   
>