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Date:   Thu, 7 Mar 2019 06:11:43 -0800
From:   Guenter Roeck <linux@roeck-us.net>
To:     Christophe Leroy <christophe.leroy@c-s.fr>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2 03/10] powerpc/6xx: Store PGDIR physical address in a
 SPRG
Message-ID: <20190307141143.GA26761@roeck-us.net>
References: <cover.1550745320.git.christophe.leroy@c-s.fr>
 <297f30d8ba75cb0e9ebe0a776d96c19750105570.1550745320.git.christophe.leroy@c-s.fr>
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In-Reply-To: <297f30d8ba75cb0e9ebe0a776d96c19750105570.1550745320.git.christophe.leroy@c-s.fr>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi,

On Thu, Feb 21, 2019 at 10:37:55AM +0000, Christophe Leroy wrote:
> Use SPRN_SPRG2 to store the current thread PGDIR and
> avoid reading thread_struct.pgdir at every TLB miss.
> 
This patch causes a number of silent (no crash) qemu boot stalls
in -next. See
https://kerneltests.org/builders/qemu-ppc-next/builds/1080/steps/qemubuildcommand/logs/stdio
for an example.

Unfortunately, it is not possible to revert the patch due to subsequent
patches, so I was unable to test a revert.

Bisect log is attached.

Guenter

---
# bad: [cf08baa29613dd899954089e7cc7dba1d478b365] Add linux-next specific files for 20190306
# good: [1c163f4c7b3f621efff9b28a47abb36f7378d783] Linux 5.0
git bisect start 'HEAD' 'v5.0'
# bad: [6cc8f3499ec8d31904ab9083980a91736512cb37] Merge remote-tracking branch 'vfs/for-next'
git bisect bad 6cc8f3499ec8d31904ab9083980a91736512cb37
# good: [63bdf4284c38a48af21745ceb148a087b190cd21] Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6
git bisect good 63bdf4284c38a48af21745ceb148a087b190cd21
# good: [520b5fc601ab760fee7ea0c403b42d04e8ebfd93] Merge remote-tracking branch 'arm-soc/for-next'
git bisect good 520b5fc601ab760fee7ea0c403b42d04e8ebfd93
# bad: [d7f54e4e0d4e90f5df78da8d6a830bafad3b535a] Merge remote-tracking branch 'xtensa/xtensa-for-next'
git bisect bad d7f54e4e0d4e90f5df78da8d6a830bafad3b535a
# good: [0c1a78523542fb3d2e6c5ac7955c8ca8f6482e6f] Merge remote-tracking branch 'clk/clk-next'
git bisect good 0c1a78523542fb3d2e6c5ac7955c8ca8f6482e6f
# bad: [fb0b0a73b223fc113e961b1d921322844e9c30d9] powerpc: Enable kcov
git bisect bad fb0b0a73b223fc113e961b1d921322844e9c30d9
# good: [d0055df0c9c1471c389197a69f43e300185a75aa] Merge branch 'topic/dma' into next
git bisect good d0055df0c9c1471c389197a69f43e300185a75aa
# good: [0df977eafc792a5365a7f81d8d5920132e03afad] powerpc/6xx: Don't use SPRN_SPRG2 for storing stack pointer while in RTAS
git bisect good 0df977eafc792a5365a7f81d8d5920132e03afad
# bad: [665bed2386e5dc29844ad78c7ef1464664b103ec] powerpc/8xx: replace most #ifdef by IS_ENABLED() in 8xx_mmu.c
git bisect bad 665bed2386e5dc29844ad78c7ef1464664b103ec
# bad: [78ca1108b10927b3d068c8da91352b0f4cd01fc5] powerpc/book3s32: Reorder _PAGE_XXX flags to simplify TLB handling
git bisect bad 78ca1108b10927b3d068c8da91352b0f4cd01fc5
# bad: [a8a121995b2e4f227fddc534c6bd5f1c02cbe2ee] powerpc/603: Don't handle kernel page TLB misses when not need
git bisect bad a8a121995b2e4f227fddc534c6bd5f1c02cbe2ee
# bad: [2c12393f577396a51b7e0537bd3eb29dcc26dc1b] powerpc/603: use physical address directly in TLB miss handlers.
git bisect bad 2c12393f577396a51b7e0537bd3eb29dcc26dc1b
# bad: [93c4a162b014d238a287f8264adb25c009c79e61] powerpc/6xx: Store PGDIR physical address in a SPRG
git bisect bad 93c4a162b014d238a287f8264adb25c009c79e61
# first bad commit: [93c4a162b014d238a287f8264adb25c009c79e61] powerpc/6xx: Store PGDIR physical address in a SPRG