Excerpts from Daniel Axtens's message of February 26, 2021 3:44 pm: > Nicholas Piggin <npiggin@xxxxxxxxx> writes: > >> The code being executed in KVM_GUEST_MODE_SKIP is hypervisor code with >> MSR[IR]=0, so the faults of concern are the d-side ones caused by access >> to guest context by the hypervisor. >> >> Instruction breakpoint interrupts are not a concern here. It's unlikely >> any good would come of causing breaks in this code, but skipping the >> instruction that caused it won't help matters (e.g., skip the mtmsr that >> sets MSR[DR]=0 or clears KVM_GUEST_MODE_SKIP). > > I'm not entirely clear on the example here, but the patch makes sense > and I can follow your logic for removing the IKVM_SKIP handler from the > instruction breakpoint exception. The example just means that a breakpoint interrupt on any instruction inside the guest mode skip region would be skipped, and skipping one of those (mtmsrd or store that gets us out of guest mode skip) would cause a crash. Thanks, Nick > > On that basis: > Reviewed-by: Daniel Axtens <dja@xxxxxxxxxx> > > Kind regards, > Daniel > >> >> Reviewed-by: Fabiano Rosas <farosas@xxxxxxxxxxxxx> >> Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx> >> --- >> arch/powerpc/kernel/exceptions-64s.S | 1 - >> 1 file changed, 1 deletion(-) >> >> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S >> index a027600beeb1..0097e0676ed7 100644 >> --- a/arch/powerpc/kernel/exceptions-64s.S >> +++ b/arch/powerpc/kernel/exceptions-64s.S >> @@ -2553,7 +2553,6 @@ EXC_VIRT_NONE(0x5200, 0x100) >> INT_DEFINE_BEGIN(instruction_breakpoint) >> IVEC=0x1300 >> #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE >> - IKVM_SKIP=1 >> IKVM_REAL=1 >> #endif >> INT_DEFINE_END(instruction_breakpoint) >> -- >> 2.23.0 >
