Re: [PATCH v2] KVM: PPC: Book3S HV: Handle guest-caused machine checks on POWER7 without panicking

[Paul Mackerras <paulus@samba.org>]

On Tue, Nov 27, 2012 at 12:16:28AM +0100, Alexander Graf wrote:
> 
> On 24.11.2012, at 09:37, Paul Mackerras wrote:
> 
> > Currently, if a machine check interrupt happens while we are in the
> > guest, we exit the guest and call the host's machine check handler,
> > which tends to cause the host to panic.  Some machine checks can be
> > triggered by the guest; for example, if the guest creates two entries
> > in the SLB that map the same effective address, and then accesses that
> > effective address, the CPU will take a machine check interrupt.
> > 
> > To handle this better, when a machine check happens inside the guest,
> > we call a new function, kvmppc_realmode_machine_check(), while still in
> > real mode before exiting the guest.  On POWER7, it handles the cases
> > that the guest can trigger, either by flushing and reloading the SLB,
> > or by flushing the TLB, and then it delivers the machine check interrupt
> > directly to the guest without going back to the host.  On POWER7, the
> > OPAL firmware patches the machine check interrupt vector so that it
> > gets control first, and it leaves behind its analysis of the situation
> > in a structure pointed to by the opal_mc_evt field of the paca.  The
> > kvmppc_realmode_machine_check() function looks at this, and if OPAL
> > reports that there was no error, or that it has handled the error, we
> > also go straight back to the guest with a machine check.  We have to
> > deliver a machine check to the guest since the machine check interrupt
> > might have trashed valid values in SRR0/1.
> > 
> > If the machine check is one we can't handle in real mode, and one that
> > OPAL hasn't already handled, or on PPC970, we exit the guest and call
> > the host's machine check handler.  We do this by jumping to the
> > machine_check_fwnmi label, rather than absolute address 0x200, because
> > we don't want to re-execute OPAL's handler on POWER7.  On PPC970, the
> > two are equivalent because address 0x200 just contains a branch.
> > 
> > Then, if the host machine check handler decides that the system can
> > continue executing, kvmppc_handle_exit() delivers a machine check
> > interrupt to the guest -- once again to let the guest know that SRR0/1
> > have been modified.
> > 
> > Signed-off-by: Paul Mackerras <paulus@samba.org>
> 
> Thanks for the semantic explanations :). From that POV things are clear and good with me now. That leaves only checkpatch ;)
> 
> 
> WARNING: please, no space before tabs
> #142: FILE: arch/powerpc/kvm/book3s_hv_ras.c:21:
> +#define SRR1_MC_IFETCH_SLBMULTI ^I3^I/* SLB multi-hit */$
> 
> WARNING: please, no space before tabs
> #143: FILE: arch/powerpc/kvm/book3s_hv_ras.c:22:
> +#define SRR1_MC_IFETCH_SLBPARMULTI ^I4^I/* SLB parity + multi-hit */$
> 
> WARNING: min() should probably be min_t(u32, slb->persistent, SLB_MIN_SIZE)
> #168: FILE: arch/powerpc/kvm/book3s_hv_ras.c:47:
> +	n = min(slb->persistent, (u32) SLB_MIN_SIZE);
> 
> total: 0 errors, 3 warnings, 357 lines checked

Phooey.  Do you want me to resubmit the patch, or will you fix it up?

Paul.