On Tue, Mar 23, 2021 at 11:02:32AM +1000, Nicholas Piggin wrote: > Move the GUEST_MODE_SKIP logic into KVM code. This is quite a KVM > internal detail that has no real need to be in common handlers. > > Also add a comment explaining why this thing exists. [snip] > diff --git a/arch/powerpc/kvm/book3s_64_entry.S b/arch/powerpc/kvm/book3s_64_entry.S > index 7a039ea78f15..a5412e24cc05 100644 > --- a/arch/powerpc/kvm/book3s_64_entry.S > +++ b/arch/powerpc/kvm/book3s_64_entry.S > @@ -1,6 +1,7 @@ > /* SPDX-License-Identifier: GPL-2.0-only */ > #include <asm/asm-offsets.h> > #include <asm/cache.h> > +#include <asm/exception-64s.h> > #include <asm/kvm_asm.h> > #include <asm/kvm_book3s_asm.h> > #include <asm/ppc_asm.h> > @@ -20,9 +21,12 @@ kvmppc_interrupt: > * guest R12 saved in shadow VCPU SCRATCH0 > * guest R13 saved in SPRN_SCRATCH0 > */ > -#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE > std r9,HSTATE_SCRATCH2(r13) > lbz r9,HSTATE_IN_GUEST(r13) > + cmpwi r9,KVM_GUEST_MODE_SKIP > + beq- .Lmaybe_skip > +.Lno_skip: > +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE > cmpwi r9,KVM_GUEST_MODE_HOST_HV > beq kvmppc_bad_host_intr > #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE > @@ -34,3 +38,48 @@ kvmppc_interrupt: > #else > b kvmppc_interrupt_pr > #endif It's a bit hard to see without more context, but I think that in the PR-only case (CONFIG_KVM_BOOK3S_HV_POSSIBLE undefined), this will corrupt R9. You need to restore R9 before the unconditional branch to kvmppc_interrupt_pr. (I realize this code gets modified further, but I'd rather not break bisection.) Paul.
