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

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, May 16, 2019 at 08:58:14AM +0200, Greg Kurz wrote:
> On Thu, 16 May 2019 12:09:57 +0530
> Satheesh Rajendran <sathnaga@linux.vnet.ibm.com> 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 <sathnaga@linux.vnet.ibm.com>
> > > Signed-off-by: Greg Kurz <groug@kaod.org>
> > > ---
> > >  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.

I won't be sending a pull request for a little while yet, so if you
want to send a followup improving the messages I can fold it into the
original patch in my tree.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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