Re: [PATCH] KVM: PPC: Book3S HV: Check for updated HDSISR on P9 HDSI exception

[Paolo Bonzini <pbonzini@redhat.com>]

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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@neuling.org>
>>> ---
>>>  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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