Re: next/master bisection: baseline.login on ox820-cloudengines-pogoplug-series-3

From: Guillaume Tucker
Date: Fri Dec 18 2020 - 08:48:58 EST

Hi Ard,

Please see the bisection report below about a boot failure on
ox820-cloudengines-pogoplug-series-3. There was also a bisection
yesterday with next-20201216 which landed on the same commit, on
the same platform and also with oxnas_v6_defconfig. I'm not
aware of any other platform on kernelci.org showing the same
regression.

Hope this helps!

Best wishes,
Guillaume

On 18/12/2020 10:51, KernelCI bot wrote:
> * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
> * This automated bisection report was sent to you on the basis *
> * that you may be involved with the breaking commit it has *
> * found. No manual investigation has been done to verify it, *
> * and the root cause of the problem may be somewhere else. *
> * *
> * If you do send a fix, please include this trailer: *
> * Reported-by: "kernelci.org bot" <bot@xxxxxxxxxxxx> *
> * *
> * Hope this helps! *
> * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
>
> next/master bisection: baseline.login on ox820-cloudengines-pogoplug-series-3
>
> Summary:
> Start: 90cc8cf2d1ab Add linux-next specific files for 20201217
> Plain log: https://storage.kernelci.org/next/master/next-20201217/arm/oxnas_v6_defconfig/gcc-8/lab-baylibre/baseline-ox820-cloudengines-pogoplug-series-3.txt
> HTML log: https://storage.kernelci.org/next/master/next-20201217/arm/oxnas_v6_defconfig/gcc-8/lab-baylibre/baseline-ox820-cloudengines-pogoplug-series-3.html
> Result: f77ac2e378be ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode
>
> Checks:
> revert: PASS
> verify: PASS
>
> Parameters:
> Tree: next
> URL: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> Branch: master
> Target: ox820-cloudengines-pogoplug-series-3
> CPU arch: arm
> Lab: lab-baylibre
> Compiler: gcc-8
> Config: oxnas_v6_defconfig
> Test case: baseline.login
>
> Breaking commit found:
>
> -------------------------------------------------------------------------------
> commit f77ac2e378be9dd61eb88728f0840642f045d9d1
> Author: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Date: Thu Nov 19 18:09:16 2020 +0100
>
> ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode
>
> There are a couple of problems with the exception entry code that deals
> with FP exceptions (which are reported as UND exceptions) when building
> the kernel in Thumb2 mode:
> - the conditional branch to vfp_kmode_exception in vfp_support_entry()
> may be out of range for its target, depending on how the linker decides
> to arrange the sections;
> - when the UND exception is taken in kernel mode, the emulation handling
> logic is entered via the 'call_fpe' label, which means we end up using
> the wrong value/mask pairs to match and detect the NEON opcodes.
>
> Since UND exceptions in kernel mode are unlikely to occur on a hot path
> (as opposed to the user mode version which is invoked for VFP support
> code and lazy restore), we can use the existing undef hook machinery for
> any kernel mode instruction emulation that is needed, including calling
> the existing vfp_kmode_exception() routine for unexpected cases. So drop
> the call to call_fpe, and instead, install an undef hook that will get
> called for NEON and VFP instructions that trigger an UND exception in
> kernel mode.
>
> While at it, make sure that the PC correction is accurate for the
> execution mode where the exception was taken, by checking the PSR
> Thumb bit.
>
> Cc: Dmitry Osipenko <digetx@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections")
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
>
> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> index c4220f51fcf3..0ea8529a4872 100644
> --- a/arch/arm/kernel/entry-armv.S
> +++ b/arch/arm/kernel/entry-armv.S
> @@ -252,31 +252,10 @@ __und_svc:
> #else
> svc_entry
> #endif
> - @
> - @ call emulation code, which returns using r9 if it has emulated
> - @ the instruction, or the more conventional lr if we are to treat
> - @ this as a real undefined instruction
> - @
> - @ r0 - instruction
> - @
> -#ifndef CONFIG_THUMB2_KERNEL
> - ldr r0, [r4, #-4]
> -#else
> - mov r1, #2
> - ldrh r0, [r4, #-2] @ Thumb instruction at LR - 2
> - cmp r0, #0xe800 @ 32-bit instruction if xx >= 0
> - blo __und_svc_fault
> - ldrh r9, [r4] @ bottom 16 bits
> - add r4, r4, #2
> - str r4, [sp, #S_PC]
> - orr r0, r9, r0, lsl #16
> -#endif
> - badr r9, __und_svc_finish
> - mov r2, r4
> - bl call_fpe
>
> mov r1, #4 @ PC correction to apply
> -__und_svc_fault:
> + THUMB( tst r5, #PSR_T_BIT ) @ exception taken in Thumb mode?
> + THUMB( movne r1, #2 ) @ if so, fix up PC correction
> mov r0, sp @ struct pt_regs *regs
> bl __und_fault
>
> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S
> index 4fcff9f59947..d5837bf05a9a 100644
> --- a/arch/arm/vfp/vfphw.S
> +++ b/arch/arm/vfp/vfphw.S
> @@ -79,11 +79,6 @@ ENTRY(vfp_support_entry)
> DBGSTR3 "instr %08x pc %08x state %p", r0, r2, r10
>
> .fpu vfpv2
> - ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions
> - and r3, r3, #MODE_MASK @ are supported in kernel mode
> - teq r3, #USR_MODE
> - bne vfp_kmode_exception @ Returns through lr
> -
> VFPFMRX r1, FPEXC @ Is the VFP enabled?
> DBGSTR1 "fpexc %08x", r1
> tst r1, #FPEXC_EN
> diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
> index 8c9e7f9f0277..c3b6451c18bd 100644
> --- a/arch/arm/vfp/vfpmodule.c
> +++ b/arch/arm/vfp/vfpmodule.c
> @@ -23,6 +23,7 @@
> #include <asm/cputype.h>
> #include <asm/system_info.h>
> #include <asm/thread_notify.h>
> +#include <asm/traps.h>
> #include <asm/vfp.h>
>
> #include "vfpinstr.h"
> @@ -642,7 +643,9 @@ static int vfp_starting_cpu(unsigned int unused)
> return 0;
> }
>
> -void vfp_kmode_exception(void)
> +#ifdef CONFIG_KERNEL_MODE_NEON
> +
> +static int vfp_kmode_exception(struct pt_regs *regs, unsigned int instr)
> {
> /*
> * If we reach this point, a floating point exception has been raised
> @@ -660,9 +663,51 @@ void vfp_kmode_exception(void)
> pr_crit("BUG: unsupported FP instruction in kernel mode\n");
> else
> pr_crit("BUG: FP instruction issued in kernel mode with FP unit disabled\n");
> + pr_crit("FPEXC == 0x%08x\n", fmrx(FPEXC));
> + return 1;
> }
>
> -#ifdef CONFIG_KERNEL_MODE_NEON
> +static struct undef_hook vfp_kmode_exception_hook[] = {{
> + .instr_mask = 0xfe000000,
> + .instr_val = 0xf2000000,
> + .cpsr_mask = MODE_MASK | PSR_T_BIT,
> + .cpsr_val = SVC_MODE,
> + .fn = vfp_kmode_exception,
> +}, {
> + .instr_mask = 0xff100000,
> + .instr_val = 0xf4000000,
> + .cpsr_mask = MODE_MASK | PSR_T_BIT,
> + .cpsr_val = SVC_MODE,
> + .fn = vfp_kmode_exception,
> +}, {
> + .instr_mask = 0xef000000,
> + .instr_val = 0xef000000,
> + .cpsr_mask = MODE_MASK | PSR_T_BIT,
> + .cpsr_val = SVC_MODE | PSR_T_BIT,
> + .fn = vfp_kmode_exception,
> +}, {
> + .instr_mask = 0xff100000,
> + .instr_val = 0xf9000000,
> + .cpsr_mask = MODE_MASK | PSR_T_BIT,
> + .cpsr_val = SVC_MODE | PSR_T_BIT,
> + .fn = vfp_kmode_exception,
> +}, {
> + .instr_mask = 0x0c000e00,
> + .instr_val = 0x0c000a00,
> + .cpsr_mask = MODE_MASK,
> + .cpsr_val = SVC_MODE,
> + .fn = vfp_kmode_exception,
> +}};
> +
> +static int __init vfp_kmode_exception_hook_init(void)
> +{
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(vfp_kmode_exception_hook); i++)
> + register_undef_hook(&vfp_kmode_exception_hook[i]);
> + return 0;
> +}
> +core_initcall(vfp_kmode_exception_hook_init);
>
> /*
> * Kernel-side NEON support functions
> -------------------------------------------------------------------------------
>
>
> Git bisection log:
>
> -------------------------------------------------------------------------------
> git bisect start
> # good: [31f6551ad75608d9c71fd4d3548c33f1abc52093] cifs: handle "guest" mount parameter
> git bisect good 31f6551ad75608d9c71fd4d3548c33f1abc52093
> # bad: [90cc8cf2d1ab87d708ebc311ac104ccbbefad9fc] Add linux-next specific files for 20201217
> git bisect bad 90cc8cf2d1ab87d708ebc311ac104ccbbefad9fc
> # good: [3db1a3fa98808aa90f95ec3e0fa2fc7abf28f5c9] Merge tag 'staging-5.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging
> git bisect good 3db1a3fa98808aa90f95ec3e0fa2fc7abf28f5c9
> # bad: [4538b80cd2885c885e3bf06e5103bc0f214c11ee] Merge remote-tracking branch 'arm-soc/for-next'
> git bisect bad 4538b80cd2885c885e3bf06e5103bc0f214c11ee
> # good: [5ee863bec794f30bdf7fdf57ce0d9f579b0d1aa3] Merge branch 'parisc-5.11-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux
> git bisect good 5ee863bec794f30bdf7fdf57ce0d9f579b0d1aa3
> # good: [fb10b701887b9fce88aacc06ca4b6c9160ca7a66] Merge branch 'arm/dt' into for-next
> git bisect good fb10b701887b9fce88aacc06ca4b6c9160ca7a66
> # good: [821a8a63a6b55ee5325e07bf5ab7d7a1752009d1] Merge remote-tracking branch 'asm-generic/master'
> git bisect good 821a8a63a6b55ee5325e07bf5ab7d7a1752009d1
> # good: [7debceff46eef5350bf2b62494c7772f78b22257] Merge branch 'arm/dt' into for-next
> git bisect good 7debceff46eef5350bf2b62494c7772f78b22257
> # bad: [b383a1412e0df59c556abb93c1fa2399e91b6102] Merge remote-tracking branch 'arm64/for-next/core'
> git bisect bad b383a1412e0df59c556abb93c1fa2399e91b6102
> # good: [113eb4ce4fc33ef3deda1431497811d43342c0cc] Merge branch 'for-next/iommu/vt-d' into for-next/iommu/core
> git bisect good 113eb4ce4fc33ef3deda1431497811d43342c0cc
> # skip: [eb86b15a2c53e2263b7cbad00a0100c8451989dc] Merge branches 'fixes' and 'misc' into for-next
> git bisect skip eb86b15a2c53e2263b7cbad00a0100c8451989dc
> # skip: [2a50d6b9cfe96ef5d39b9c3497dcc83a907d00cd] ARM: 9033/1: arm/smp: Drop the macro S(x,s)
> git bisect skip 2a50d6b9cfe96ef5d39b9c3497dcc83a907d00cd
> # good: [421015713b306e47af95d4d61cdfbd96d462e4cb] ARM: 9017/2: Enable KASan for ARM
> git bisect good 421015713b306e47af95d4d61cdfbd96d462e4cb
> # good: [2c736bb4087f2cb949cbbaf4148733131b8466dc] Merge tag 'arm-adrl-replacement-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux into devel-stable
> git bisect good 2c736bb4087f2cb949cbbaf4148733131b8466dc
> # skip: [3597a10e4c444f3d4d6a64bdc98e4585a99301b9] ARM: 9036/1: uncompress: Fix dbgadtb size parameter name
> git bisect skip 3597a10e4c444f3d4d6a64bdc98e4585a99301b9
> # skip: [1205285c7a71c3b7a879e31ec477639f2dac22b1] ARM: 9027/1: head.S: explicitly map DT even if it lives in the first physical section
> git bisect skip 1205285c7a71c3b7a879e31ec477639f2dac22b1
> # good: [71fe89ceb55bc0a85121b757cc8d3fb6ff457263] dma-iommu: remove __iommu_dma_mmap
> git bisect good 71fe89ceb55bc0a85121b757cc8d3fb6ff457263
> # skip: [17fb1a208129e3472ec45be08cbe39601a407e2c] ARM: 9031/1: hyp-stub: remove unused .L__boot_cpu_mode_offset symbol
> git bisect skip 17fb1a208129e3472ec45be08cbe39601a407e2c
> # good: [95d1718c961e49cfa02995ce1587a22cd7e2fbf5] Merge remote-tracking branch 'arm64/for-next/iommu/core' into for-next/core
> git bisect good 95d1718c961e49cfa02995ce1587a22cd7e2fbf5
> # skip: [0fe88ade3f937d6efc276901a56be6575a5a2171] ARM: 9032/1: arm/mm: Convert PUD level pgtable helper macros into functions
> git bisect skip 0fe88ade3f937d6efc276901a56be6575a5a2171
> # good: [730b5764ea8526e48bdb85a24ed96d62de435940] ARM: 9024/1: Drop useless cast of "u64" to "long long"
> git bisect good 730b5764ea8526e48bdb85a24ed96d62de435940
> # good: [4d576cab16f57e1f87978f6997a725179398341e] ARM: 9028/1: disable KASAN in call stack capturing routines
> git bisect good 4d576cab16f57e1f87978f6997a725179398341e
> # skip: [3bdf1a7503d61d2241f93f36e9c0d8a0d444bc5c] ARM: 9037/1: uncompress: Add OF_DT_MAGIC macro
> git bisect skip 3bdf1a7503d61d2241f93f36e9c0d8a0d444bc5c
> # bad: [f77ac2e378be9dd61eb88728f0840642f045d9d1] ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode
> git bisect bad f77ac2e378be9dd61eb88728f0840642f045d9d1
> # good: [3c9f5708b7aed6a963e2aefccbd1854802de163e] ARM: 9029/1: Make iwmmxt.S support Clang's integrated assembler
> git bisect good 3c9f5708b7aed6a963e2aefccbd1854802de163e
> # first bad commit: [f77ac2e378be9dd61eb88728f0840642f045d9d1] ARM: 9030/1: entry: omit FP emulation for UND exceptions taken in kernel mode
> -------------------------------------------------------------------------------
>
>
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