Re: [PATCH] KVM: PPC: Book3S HV: Treat TM-related invalid form instructions on P9 like the valid ones

[Gustavo Romero]

Hi Leonardo,

Thanks a lot for the review.

On 02/20/2020 02:51 PM, Leonardo Bras wrote:

+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+

Could not see where is this used.

This is used by pr_warn_ratelimited() below so the module name is printed before
the message, for instance:

[531454.670909] kvm_hv: Unrecognized TM-related instruction 0x7c00075c for 
emulation

  #include <linux/kvm_host.h>

  #include <asm/kvm_ppc.h>
@@ -44,7 +46,18 @@ int kvmhv_p9_tm_emulation(struct kvm_vcpu *vcpu)
        u64 newmsr, bescr;
        int ra, rs;

-       switch (instr & 0xfc0007ff) {
+       /*
+        * rfid, rfebb, and mtmsrd encode bit 31 = 0 since it's a reserved bit
+        * in these instructions, so masking bit 31 out doesn't change these
+        * instructions. For treclaim., tsr., and trechkpt. instructions if bit
+        * 31 = 0 then they are per ISA invalid forms, however P9 UM, in section
+        * 4.6.10 Book II Invalid Forms, informs specifically that ignoring bit
+        * 31 is an acceptable way to handle these invalid forms that have
+        * bit 31 = 0. Moreover, for emulation purposes both forms (w/ and wo/
+        * bit 31 set) can generate a softpatch interrupt. Hence both forms
+        * are handled below for these instructions so they behave the same way.
+        */
+       switch (instr & PO_XOP_OPCODE_MASK) {

<SNIP>

-       case PPC_INST_TRECHKPT:
+       /* ignore bit 31, see comment above */
+       case (PPC_INST_TRECHKPT & PO_XOP_OPCODE_MASK):
                /* XXX do we need to check for PR=0 here? */
                /* check for TM disabled in the HFSCR or MSR */
                if (!(vcpu->arch.hfscr & HFSCR_TM)) {
@@ -208,6 +224,8 @@ int kvmhv_p9_tm_emulation(struct kvm_vcpu *vcpu)
        }

Seems good, using the same flag to mask out bit 31 of these macros.
They are used only in a few places, and I think removing the macro bit
would be ok, but I think your way is better to keep it documented.

I just noticed that there is a similar function that uses PPC_INST_TSR:
kvmhv_p9_tm_emulation_early @ arch/powerpc/kvm/book3s_hv_tm_builtin.c.
Wouldn't it need to be changed as well?

oh! you're right, I forgot that one. I'll send a v3.

        /* 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;
  }

I suppose this is the right thing to do, but I think it would be better
to give this change it's own patch.

What do you think?

I think it's sufficiently self-contained and trivial to be in the same file and
to be in a single commit.


Best regards,
Gustavo