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Tue, 31 Aug 2021 23:48:21 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ellerman.id.au; s=201909; t=1630417701; bh=8oS99HH6AUTzOOju4RU630SDk6FIxjIbOfVXLSa66Es=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=L3RWeaXku45++htSouP4mrMXDNz5yFXKq9mzsKd6kTnL6wzaehAxuzUTwEgoJcjh/ ydUo5b9sfW/CaL6BsJeWawe6ne7IN/i2doLdHtR32QbaSGoXtdzWqN9zoJKB7U3dfd cqAjKgQYmL/3qAsG1VoNS6tXkM+U+tVA6EhC2A+wwFC0FuNxfU/dcgMezZO8OECyxG KDrFQSrgric1Z+12zz447pYXZYvDqFIkpYoyipZhlmR/7s1evjtVGsgp3fQ9yCvgXI dm3BllEAZ45Q74rw06gobE0SV5sbLA20BWKR20Z6FTcbr9T/7vCrbyL3my5L4WTAtb C3ujLJAL2jilA== From: Michael Ellerman To: Christophe Leroy , Nathan Chancellor Cc: Benjamin Herrenschmidt , Paul Mackerras , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v4 4/4] powerpc/ptdump: Convert powerpc to GENERIC_PTDUMP In-Reply-To: <55783e78-3159-9ab2-7955-fb5aa8aa0ddd@csgroup.eu> References: <03166d569526be70214fe9370a7bad219d2f41c8.1625762907.git.christophe.leroy@csgroup.eu> <5c479866-f31a-3579-9d71-357c85b777d0@csgroup.eu> <87tuj7e5e5.fsf@mpe.ellerman.id.au> <2bd9fa19-07b0-c187-c7dd-c6d544e34739@csgroup.eu> <87r1ebdu4t.fsf@mpe.ellerman.id.au> <55783e78-3159-9ab2-7955-fb5aa8aa0ddd@csgroup.eu> Date: Tue, 31 Aug 2021 23:48:17 +1000 Message-ID: <87mtoxendq.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christophe Leroy writes: > Le 30/08/2021 =C3=A0 13:55, Michael Ellerman a =C3=A9crit=C2=A0: >> Christophe Leroy writes: >>> Le 30/08/2021 =C3=A0 09:52, Michael Ellerman a =C3=A9crit=C2=A0: >>>> Christophe Leroy writes: >>>>> Le 29/08/2021 =C3=A0 20:55, Nathan Chancellor a =C3=A9crit=C2=A0: >>>>>> On Thu, Jul 08, 2021 at 04:49:43PM +0000, Christophe Leroy wrote: >>>>>>> This patch converts powerpc to the generic PTDUMP implementation. >>>>>>> >>>>>> >>>>>> This patch as commit e084728393a5 ("powerpc/ptdump: Convert powerpc = to >>>>>> GENERIC_PTDUMP") in powerpc/next causes a panic with Fedora's ppc64le >>>>>> config [1] when booting up in QEMU with [2]: >>>>>> >>>>>> [ 1.621864] BUG: Unable to handle kernel data access on read at 0= xc0eeff7f00000000 >>>>>> [ 1.623058] Faulting instruction address: 0xc00000000045e5fc >>>>>> [ 1.623832] Oops: Kernel access of bad area, sig: 11 [#1] >>>>>> [ 1.624318] LE PAGE_SIZE=3D64K MMU=3DHash SMP NR_CPUS=3D2048 NUMA= PowerNV >>>>>> [ 1.625015] Modules linked in: >>>>>> [ 1.625463] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.14.0-rc7-= next-20210827 #16 >>>>>> [ 1.626237] NIP: c00000000045e5fc LR: c00000000045e580 CTR: c000= 000000518220 >>>>>> [ 1.626839] REGS: c00000000752b820 TRAP: 0380 Not tainted (5.1= 4.0-rc7-next-20210827) >>>>>> [ 1.627528] MSR: 9000000002009033 = CR: 84002482 XER: 20000000 >>>>>> [ 1.628449] CFAR: c000000000518300 IRQMASK: 0 >>>>>> [ 1.628449] GPR00: c00000000045e580 c00000000752bac0 c0000000028a= 9300 0000000000000000 >>>>>> [ 1.628449] GPR04: c200800000000000 ffffffffffffffff 000000000000= 000a 0000000000000001 >>>>>> [ 1.628449] GPR08: c0eeff7f00000000 0000000000000012 000000000000= 0000 0000000000000000 >>>>>> [ 1.628449] GPR12: 0000000000000000 c000000002b20000 ffffffffffff= fffe c000000002971a70 >>>>>> [ 1.628449] GPR16: c000000002960040 c0000000011a8f98 c00000000752= bbf0 ffffffffffffffff >>>>>> [ 1.628449] GPR20: c2008fffffffffff c0eeff7f00000000 c00000000297= 1a68 c00a0003ff000000 >>>>>> [ 1.628449] GPR24: c000000002971a78 0000000000000002 000000000000= 0001 c0000000011a8f98 >>>>>> [ 1.628449] GPR28: c0000000011a8f98 c0000000028daef8 c20080000000= 0000 c200900000000000 >>>>>> [ 1.634090] NIP [c00000000045e5fc] __walk_page_range+0x2bc/0xce0 >>>>>> [ 1.635117] LR [c00000000045e580] __walk_page_range+0x240/0xce0 >>>>>> [ 1.635755] Call Trace: >>>>>> [ 1.636018] [c00000000752bac0] [c00000000045e580] __walk_page_ran= ge+0x240/0xce0 (unreliable) >>>>>> [ 1.636811] [c00000000752bbd0] [c00000000045f234] walk_page_range= _novma+0x74/0xb0 >>>>>> [ 1.637459] [c00000000752bc20] [c000000000518448] ptdump_walk_pgd= +0x98/0x170 >>>>>> [ 1.638138] [c00000000752bc70] [c0000000000aa988] ptdump_check_wx= +0x88/0xd0 >>>>>> [ 1.638738] [c00000000752bd50] [c00000000008d6d8] mark_rodata_ro+= 0x48/0x80 >>>>>> [ 1.639299] [c00000000752bdb0] [c000000000012a34] kernel_init+0x7= 4/0x1a0 >>>>>> [ 1.639842] [c00000000752be10] [c00000000000cfd4] ret_from_kernel= _thread+0x5c/0x64 >>>>>> [ 1.640597] Instruction dump: >>>>>> [ 1.641021] 38e7ffff 39490010 7ce707b4 7fca5436 79081564 7d4a3838= 7908f082 794a1f24 >>>>>> [ 1.641740] 78a8f00e 30e6ffff 7ea85214 7ce73110 <7d48502a> 78f90f= a4 2c2a0000 39290010 >>>>>> [ 1.642771] ---[ end trace 6cf72b085097ad52 ]--- >>>>>> [ 1.643220] >>>>>> [ 2.644228] Kernel panic - not syncing: Attempted to kill init! e= xitcode=3D0x0000000b >>>>>> [ 2.645523] ---[ end Kernel panic - not syncing: Attempted to kil= l init! exitcode=3D0x0000000b ]--- >>>>>> >>>>>> This is not compiler specific, I can reproduce it with GCC 11.2.0 and >>>>>> binutils 2.37. If there is any additional information I can provide, >>>>>> please let me know. >>>>> >>>>> Can you provide a dissassembly of __walk_page_range() ? Or provide yo= ur vmlinux binary. >>>> >>>> It seems to be walking of the end of the pgd. >>>> >>>> [ 3.373800] walk_p4d_range: addr c00fff0000000000 end c00fff8000000= 000 >>>> [ 3.373852] walk_p4d_range: addr c00fff8000000000 end c010000000000= 000 <- end of pgd at PAGE_OFFSET + 4PB >>>> [ 3.373905] walk_p4d_range: addr c010000000000000 end c010008000000= 000 >>> >>> Yes, I want it to walk from TASK_SIZE_MAX up to 0xffffffffffffffff :) >>=20 >> But the page table doesn't span that far? 0_o >>=20 >>> static struct ptdump_range ptdump_range[] __ro_after_init =3D { >>> {TASK_SIZE_MAX, ~0UL}, >>> {0, 0} >>> }; >>> >>> Ok, well, ppc32 go up to 0xffffffff >>> >>> What's the top address to be used for ppc64 ? >>=20 >> It's different for (hash | radix) x page size. >>=20 >> The below works, and matches what we used to do. >>=20 >> Possibly we can come up with something cleaner, not sure. >>=20 >> cheers >>=20 >>=20 >> diff --git a/arch/powerpc/mm/ptdump/ptdump.c b/arch/powerpc/mm/ptdump/pt= dump.c >> index 2d80d775d15e..3d3778a74969 100644 >> --- a/arch/powerpc/mm/ptdump/ptdump.c >> +++ b/arch/powerpc/mm/ptdump/ptdump.c >> @@ -359,6 +359,8 @@ static int __init ptdump_init(void) >> ptdump_range[0].start =3D KERN_VIRT_START; >> else >> ptdump_range[0].start =3D PAGE_OFFSET; >> + >> + ptdump_range[0].end =3D ptdump_range[0].start + (PGDIR_SIZE * PTRS_PER= _PGD); > > Hum ... > > It was: > > for (i =3D pgd_index(addr); i < PTRS_PER_PGD; i++, pgd++, addr +=3D PGDI= R_SIZE) { > > And there is > > #define pgd_index(a) (((a) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1)) Yes you're right. > Do we have the following ? > > pgd_index(KERN_VIRT_START) =3D=3D 0 No. Since 0034d395f89d ("powerpc/mm/hash64: Map all the kernel regions in the s= ame 0xc range") It's: pgd_index(PAGE_OFFSET) =3D=3D 0 > Shouldn't it be something like > > ptdump_range[0].end =3D PAGE_OFFSET + (PGDIR_SIZE * PTRS_PER_PGD); Yep. And we should also change the start address for hash to be PAGE_OFFSET. Even though we don't expect anything in the page tables between PAGE_OFFSET and KERN_VIRT_START, it's still good to check that range. cheers