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Date: Tue, 19 Feb 2019 14:13:51 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v6] powerpc/64s: reimplement book3s idle code in C
To: Paul Mackerras <paulus@ozlabs.org>
References: <20181013120409.1993-1-npiggin@gmail.com>
 <20190217230640.GA922@blackberry>
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Cc: "Gautham R . Shenoy" <ego@linux.vnet.ibm.com>,
 Mahesh Jagannath Salgaonkar <mahesh@linux.vnet.ibm.com>,
 kvm-ppc@vger.kernel.org, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
 linuxppc-dev@lists.ozlabs.org, Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Paul Mackerras's on February 18, 2019 9:06 am:
> On Sat, Oct 13, 2018 at 10:04:09PM +1000, Nicholas Piggin wrote:
>> Reimplement Book3S idle code in C, moving POWER7/8/9 implementation
>> speific HV idle code to the powernv platform code.
>>=20
>=20
> [...]
>=20
>> @@ -2760,21 +2744,47 @@ BEGIN_FTR_SECTION
>>  	li	r4, LPCR_PECE_HVEE@higher
>>  	sldi	r4, r4, 32
>>  	or	r5, r5, r4
>> -END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
>> +FTR_SECTION_ELSE
>> +	li	r3, PNV_THREAD_NAP
>> +ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_300)
>>  	mtspr	SPRN_LPCR,r5
>>  	isync
>> -	li	r0, 0
>> -	std	r0, HSTATE_SCRATCH0(r13)
>> -	ptesync
>> -	ld	r0, HSTATE_SCRATCH0(r13)
>> -1:	cmpd	r0, r0
>> -	bne	1b
>> +
>> +	mr	r0, r1
>> +	ld	r1, PACAEMERGSP(r13)
>> +	subi	r1, r1, STACK_FRAME_OVERHEAD
>> +	std	r0, 0(r1)
>> +	ld	r0, PACAR1(r13)
>> +	std	r0, 8(r1)
>=20
> This bit seems wrong to me.  If this is a secondary thread on POWER8,
> we were already on the emergency stack, and now we've reset r1 back to
> the top of the emergency stack and we're overwriting it.

I'll have to find some time to take another look at this stuff. The KVM
stuff was a bit hasty.

> I wonder why you didn't see secondary threads going off into lala land
> in your tests?

It must have been because I wasn't testing the guest SMT properly=20
because I did get it to break trivially sometime after posting this=20
patch out. So we were on the emergency stack here, that should make
things easier, that may be what's wrong.

Thanks,
Nick

=

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicholas Piggin <npiggin@gmail.com>
Date: Tue, 19 Feb 2019 04:13:51 +0000
Subject: Re: [PATCH v6] powerpc/64s: reimplement book3s idle code in C
Message-Id: <1550549470.22tqiqz5em.astroid@bobo.none>
List-Id: <kvm-ppc.vger.kernel.org>
References: <20181013120409.1993-1-npiggin@gmail.com>
 <20190217230640.GA922@blackberry>
In-Reply-To: <20190217230640.GA922@blackberry>
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To: Paul Mackerras <paulus@ozlabs.org>
Cc: "Gautham R . Shenoy" <ego@linux.vnet.ibm.com>, Mahesh Jagannath Salgaonkar <mahesh@linux.vnet.ibm.com>, kvm-ppc@vger.kernel.org, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>, linuxppc-dev@lists.ozlabs.org, Akshay Adiga <akshay.adiga@linux.vnet.ibm.com>

Paul Mackerras's on February 18, 2019 9:06 am:
> On Sat, Oct 13, 2018 at 10:04:09PM +1000, Nicholas Piggin wrote:
>> Reimplement Book3S idle code in C, moving POWER7/8/9 implementation
>> speific HV idle code to the powernv platform code.
>> 
> 
> [...]
> 
>> @@ -2760,21 +2744,47 @@ BEGIN_FTR_SECTION
>>  	li	r4, LPCR_PECE_HVEE@higher
>>  	sldi	r4, r4, 32
>>  	or	r5, r5, r4
>> -END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
>> +FTR_SECTION_ELSE
>> +	li	r3, PNV_THREAD_NAP
>> +ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_300)
>>  	mtspr	SPRN_LPCR,r5
>>  	isync
>> -	li	r0, 0
>> -	std	r0, HSTATE_SCRATCH0(r13)
>> -	ptesync
>> -	ld	r0, HSTATE_SCRATCH0(r13)
>> -1:	cmpd	r0, r0
>> -	bne	1b
>> +
>> +	mr	r0, r1
>> +	ld	r1, PACAEMERGSP(r13)
>> +	subi	r1, r1, STACK_FRAME_OVERHEAD
>> +	std	r0, 0(r1)
>> +	ld	r0, PACAR1(r13)
>> +	std	r0, 8(r1)
> 
> This bit seems wrong to me.  If this is a secondary thread on POWER8,
> we were already on the emergency stack, and now we've reset r1 back to
> the top of the emergency stack and we're overwriting it.

I'll have to find some time to take another look at this stuff. The KVM
stuff was a bit hasty.

> I wonder why you didn't see secondary threads going off into lala land
> in your tests?

It must have been because I wasn't testing the guest SMT properly 
because I did get it to break trivially sometime after posting this 
patch out. So we were on the emergency stack here, that should make
things easier, that may be what's wrong.

Thanks,
Nick