From: Paul Mackerras <paulus@ozlabs.org>
To: Nicholas Piggin <npiggin@gmail.com>
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>
Subject: Re: [PATCH v6] powerpc/64s: reimplement book3s idle code in C
Date: Wed, 20 Feb 2019 11:59:22 +1100 [thread overview]
Message-ID: <20190220005922.GC5353@blackberry> (raw)
In-Reply-To: <1550549470.22tqiqz5em.astroid@bobo.none>
On Tue, Feb 19, 2019 at 02:13:51PM +1000, Nicholas Piggin wrote:
> 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.
In fact I don't see why you need to load up a new stack here at all;
you could just use whatever stack we're currently on AFAICS.
Paul.
prev parent reply other threads:[~2019-02-20 1:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-13 12:04 [PATCH v6] powerpc/64s: reimplement book3s idle code in C Nicholas Piggin
2019-02-17 23:06 ` Paul Mackerras
2019-02-19 4:13 ` Nicholas Piggin
2019-02-20 0:59 ` Paul Mackerras [this message]
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