On 22/09/2017 12:30, David Gibson wrote: > On Fri, Sep 22, 2017 at 10:46:36AM +0200, Paolo Bonzini wrote: >> On 15/09/2017 07:26, Michael Neuling wrote: >>> On POWER9 DD2.1 and below, sometimes on a Hypervisor Data Storage >>> Interrupt (HDSI) the HDSISR is not be updated at all. >>> >>> To work around this we put a canary value into the HDSISR before >>> returning to a guest and then check for this canary when we take a >>> HDSI. If we find the canary on a HDSI, we know the hardware didn't >>> update the HDSISR. In this case we return to the guest to retake the >>> HDSI which should correctly update the HDSISR the second time HDSI >>> entry. >>> >>> After talking to Paulus we've applied this workaround to all POWER9 >>> CPUs. The workaround of returning to the guest shouldn't ever be >>> triggered on well behaving CPU. The extra instructions should have >>> negligible performance impact. >>> >>> Signed-off-by: Michael Neuling <mikey@xxxxxxxxxxx> >>> --- >>> arch/powerpc/kvm/book3s_hv_rmhandlers.S | 14 +++++++++++++- >>> 1 file changed, 13 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S >>> index 663a4a861e..70dca60569 100644 >>> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S >>> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S >>> @@ -1118,6 +1118,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) >>> BEGIN_FTR_SECTION >>> mtspr SPRN_PPR, r0 >>> END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) >>> + >>> +/* Move canary into DSISR to check for later */ >>> +BEGIN_FTR_SECTION >>> + li r0, 0x7fff >>> + mtspr SPRN_HDSISR, r0 >>> +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300) >>> + >>> ld r0, VCPU_GPR(R0)(r4) >>> ld r4, VCPU_GPR(R4)(r4) >>> >>> @@ -1947,9 +1954,14 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX) >>> kvmppc_hdsi: >>> ld r3, VCPU_KVM(r9) >>> lbz r0, KVM_RADIX(r3) >>> - cmpwi r0, 0 >>> mfspr r4, SPRN_HDAR >>> mfspr r6, SPRN_HDSISR >>> +BEGIN_FTR_SECTION >>> + /* Look for DSISR canary. If we find it, retry instruction */ >>> + cmpdi r6, 0x7fff >>> + beq 6f >>> +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300) >>> + cmpwi r0, 0 >>> bne .Lradix_hdsi /* on radix, just save DAR/DSISR/ASDR */ >>> /* HPTE not found fault or protection fault? */ >>> andis. r0, r6, (DSISR_NOHPTE | DSISR_PROTFAULT)@h >>> >> >> Applied to kvm/master, thanks. > > I'm not seeing it; have you pushed out the tree? No, not yet (doing some tests). Paolo
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