On Tue, Apr 04, 2017 at 12:05:03PM +0200, Thomas Huth wrote:
> According to the PowerISA 2.07, mtspr and mfspr should not always
> generate an illegal instruction exception when being used with an
> undefined SPR, but rather treat the instruction as a NOP or inject a
> privilege exception in some cases, too - depending on the SPR number.
> Also turn the printk here into a ratelimited print statement, so that
> the guest can not flood the dmesg log of the host by issueing lots of
> illegal mtspr/mfspr instruction here.
>
> Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
> ---
> v2:
> - Inject illegal instruction program interrupt instead of emulation
> assist interrupt (according to the last programming note in section
> 6.5.9 of Book III of the PowerISA v2.07)
>
> arch/powerpc/kvm/book3s_emulate.c | 26 ++++++++++++++++++--------
> 1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_emulate.c b/arch/powerpc/kvm/book3s_emulate.c
> index 8359752..bf4181e 100644
> --- a/arch/powerpc/kvm/book3s_emulate.c
> +++ b/arch/powerpc/kvm/book3s_emulate.c
> @@ -503,10 +503,14 @@ int kvmppc_core_emulate_mtspr_pr(struct kvm_vcpu *vcpu, int sprn, ulong spr_val)
> break;
> unprivileged:
> default:
> - printk(KERN_INFO "KVM: invalid SPR write: %d\n", sprn);
> -#ifndef DEBUG_SPR
> - emulated = EMULATE_FAIL;
> -#endif
> + pr_info_ratelimited("KVM: invalid SPR write: %d\n", sprn);
> + if (sprn & 0x10) {
> + if (kvmppc_get_msr(vcpu) & MSR_PR)
> + kvmppc_core_queue_program(vcpu, SRR1_PROGPRIV);
> + } else {
> + if ((kvmppc_get_msr(vcpu) & MSR_PR) || sprn == 0)
> + kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> + }
> break;
In the cases where we generate an interrupt, we are now returning
EMULATE_DONE, which means that kvmppc_emulate_instruction() will
advance the PC by 4 after this function returns. Since
kvmppc_core_queue_program() injects the interrupt straight away, this
means that the guest will resume execution at 0x704 rather than
0x700.
Paul.
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