Re: [Qemu-devel] [Qemu-ppc] [PATCH v8 4/6] target/ppc: Build rtas error log upon an MCE

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

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On Tue, May 14, 2019 at 09:56:41AM +0530, Aravinda Prasad wrote:
> 
> 
> On Tuesday 14 May 2019 05:38 AM, David Gibson wrote:
> > On Mon, May 13, 2019 at 01:30:53PM +0200, Greg Kurz wrote:
> >> On Mon, 22 Apr 2019 12:33:26 +0530
> >> Aravinda Prasad <aravinda@linux.vnet.ibm.com> wrote:
> >>
> >>> Upon a machine check exception (MCE) in a guest address space,
> >>> KVM causes a guest exit to enable QEMU to build and pass the
> >>> error to the guest in the PAPR defined rtas error log format.
> >>>
> >>> This patch builds the rtas error log, copies it to the rtas_addr
> >>> and then invokes the guest registered machine check handler. The
> >>> handler in the guest takes suitable action(s) depending on the type
> >>> and criticality of the error. For example, if an error is
> >>> unrecoverable memory corruption in an application inside the
> >>> guest, then the guest kernel sends a SIGBUS to the application.
> >>> For recoverable errors, the guest performs recovery actions and
> >>> logs the error.
> >>>
> >>> Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
> >>> ---
> >>>  hw/ppc/spapr.c         |    4 +
> >>>  hw/ppc/spapr_events.c  |  245 ++++++++++++++++++++++++++++++++++++++++++++++++
> >>>  include/hw/ppc/spapr.h |    4 +
> >>>  3 files changed, 253 insertions(+)
> >>>
> >>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> >>> index 2779efe..ffd1715 100644
> >>> --- a/hw/ppc/spapr.c
> >>> +++ b/hw/ppc/spapr.c
> >>> @@ -2918,6 +2918,10 @@ static void spapr_machine_init(MachineState *machine)
> >>>          error_report("Could not get size of LPAR rtas '%s'", filename);
> >>>          exit(1);
> >>>      }
> >>> +
> >>> +    /* Resize blob to accommodate error log. */
> >>> +    spapr->rtas_size = spapr_get_rtas_size(spapr->rtas_size);
> >>> +
> >>
> >> This is the only user for spapr_get_rtas_size(), which is trivial.
> >> I suggest you simply open-code it here.
> > 
> > I agree.
> 
> Sure.
> 
> > 
> >> But also, spapr->rtas_size is a guest visible thing, "rtas-size" prop in the
> >> DT. Since existing machine types don't do that, I guess we should only use
> >> the new size if cap-fwnmi-mce=on for the sake of compatibility.
> > 
> > Yes, that's a good idea.  Changing this is very unlikely to break a
> > guest, but it's easy to be safe here so let's do it.
> 
> I did it like that because the rtas_blob is allocated based on rtas_size
> in spapr_machine_init(). During spapr_machine_init() it is not know if
> the guest calls "ibm, nmi-register". So if we want to use the new size
> only when cap_fwnmi=on, then we have to realloc the blob in "ibm,
> nmi-register".

What?  Just always allocate the necessary space in
spapr_machine_init() if cap_fwnmi=on, it'll be wasted if
ibm,nmi-register is never called, but it's not that much space so we
don't really care.

-- 
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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