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.
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