> From: Alexander Graf <agraf@xxxxxxx> > Sent: Friday, May 2, 2014 12:24 PM > To: Caraman Mihai Claudiu-B02008 > Cc: kvm-ppc@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx > Subject: Re: [PATCH v2 1/4] KVM: PPC: e500mc: Revert "add load inst fixup" > > On 05/01/2014 02:45 AM, Mihai Caraman wrote: > > The commit 1d628af7 "add load inst fixup" made an attempt to handle > > failures generated by reading the guest current instruction. The fixup > > code that was added works by chance hiding the real issue. > > > > Load external pid (lwepx) instruction, used by KVM to read guest > > instructions, is executed in a subsituted guest translation context > > (EPLC[EGS] = 1). In consequence lwepx's TLB error and data storage > > interrupts need to be handled by KVM, even though these interrupts > > are generated from host context (MSR[GS] = 0). > > > > Currently, KVM hooks only interrupts generated from guest context > > (MSR[GS] = 1), doing minimal checks on the fast path to avoid host > > performance degradation. As a result, the host kernel handles lwepx > > faults searching the faulting guest data address (loaded in DEAR) in > > its own Logical Partition ID (LPID) 0 context. In case a host translation > > is found the execution returns to the lwepx instruction instead of the > > fixup, the host ending up in an infinite loop. > > > > Revert the commit "add load inst fixup". lwepx issue will be addressed > > in a subsequent patch without needing fixup code. > > > > Signed-off-by: Mihai Caraman <mihai.caraman@xxxxxxxxxxxxx> > > Just a random idea: Could we just switch IVOR2 during the critical lwepx > phase? In fact, we could even do that later when we're already in C code > and try to recover the last instruction. The code IVOR2 would point to > would simply set the register we're trying to read to as LAST_INST_FAIL > and rfi. This was the first idea that sprang to my mind inspired from how DO_KVM is hooked on PR. I actually did a simple POC for e500mc/e5500, but this will not work on e6500 which has shared IVORs between HW threads. -Mike-- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
