Re: [PATCH] KVM: PPC: Book3S HV: Treat unrecognized TM instructions as illegal
From: Segher Boessenkool <hidden>
Date: 2020-02-13 23:33:10
On Thu, Feb 13, 2020 at 10:15:32AM -0500, Gustavo Romero wrote:
On P9 DD2.2 due to a CPU defect some TM instructions need to be emulated by
KVM. This is handled at first by the hardware raising a softpatch interrupt
when certain TM instructions that need KVM assistance are executed in the
guest. Some TM instructions, although not defined in the Power ISA, might
raise a softpatch interrupt. For instance, 'tresume.' instruction as
defined in the ISA must have bit 31 set (1), but an instruction that
matches 'tresume.' OP and XO opcodes but has bit 31 not set (0), like
0x7cfe9ddc, also raises a softpatch interrupt, for example, if a code
like the following is executed in the guest it will raise a softpatch
interrupt just like a 'tresume.' when the TM facility is enabled:
int main() { asm("tabort. 0; .long 0x7cfe9ddc;"); }
Currently in such a case KVM throws a complete trace like the following:[snip]
and then treats the executed instruction as 'nop' whilst it should actually be treated as an illegal instruction since it's not defined by the ISA. This commit changes the handling of the case above by treating the unrecognized TM instructions that can raise a softpatch but are not defined in the ISA as illegal ones instead of as 'nop' and by gently reporting it to the host instead of throwing a trace. Signed-off-by: Gustavo Romero <redacted>
Reviewed-by: Segher Boessenkool <redacted>
quoted hunk ↗ jump to hunk
--- arch/powerpc/kvm/book3s_hv_tm.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)diff --git a/arch/powerpc/kvm/book3s_hv_tm.c b/arch/powerpc/kvm/book3s_hv_tm.c index 0db937497169..d342a9e11298 100644 --- a/arch/powerpc/kvm/book3s_hv_tm.c +++ b/arch/powerpc/kvm/book3s_hv_tm.c@@ -3,6 +3,8 @@ * Copyright 2017 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com> */ +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + #include <linux/kvm_host.h> #include <asm/kvm_ppc.h>@@ -208,6 +210,8 @@ int kvmhv_p9_tm_emulation(struct kvm_vcpu *vcpu) } /* What should we do here? We didn't recognize the instruction */ - WARN_ON_ONCE(1); + kvmppc_core_queue_program(vcpu, SRR1_PROGILL); + pr_warn_ratelimited("Unrecognized TM-related instruction %#x for emulation", instr); + return RESUME_GUEST; }
Do we actually know it is TM-related here? Otherwise, looks good to me :-) Segher