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Message-ID: <4611b3c8-0ef6-4951-8b34-10a1c7262355@leemhuis.info>
Date: Thu, 30 May 2024 09:27:34 +0200
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Subject: Re: [REGRESSION] commit fbf6449f84bf5e4ad09f2c09ee70ed7d629b5ff6
 (Linux 6.7+) crashes during boot
To: =?UTF-8?Q?J=C3=B6rn_Heusipp?= <osmanx@heusipp.de>,
 linux-kernel@vger.kernel.org
Cc: regressions@lists.linux.dev, x86@kernel.org,
 Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Dave Hansen <dave.hansen@linux.intel.com>, Borislav Petkov <bp@alien8.de>,
 Andy Lutomirski <luto@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
 Adam Dunlap <acdunlap@google.com>, 1071378@bugs.debian.org
References: <ebb0791c-60a5-4fe3-bc85-4921ad026605@heusipp.de>
From: "Linux regression tracking (Thorsten Leemhuis)"
 <regressions@leemhuis.info>
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On 30.05.24 08:55, Jörn Heusipp wrote:
> 
> Hello x86 maintainers!
> 
> commit fbf6449f84bf5e4ad09f2c09ee70ed7d629b5ff6 ("x86/sev-es: Set
> x86_virt_bits to the correct value straight away, instead of a two-phase
> approach") crashes during boot for me on this 32bit x86 system.

FWIW, not my area of expertise, but there is a patch from Dave with a
Fixes: tag for your culprit up for review:
https://lore.kernel.org/all/20240517200534.8EC5F33E@davehans-spike.ostc.intel.com/

Ciao, Thorsten

> Updating a Debian testing system resulted in a hang during boot before
> printing anything, with any 6.7 or later kernel. With 'earlyprintk=vga',
> I managed to capture the crash on video and stitched it together as an
> image [1].
> Trimmed transcription (might contain typos) of the crash from Debian
> kernel 6.7.12-1:
> ===
> BUG: kernel NULL pointer dereference, address: 00000010
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> Oops: 0002 [#1] PREEMPT SMP NOPTI
> [...]
> EIP: __ring_buffer_alloc+0x32/0x194
> [...]
> show_regs
> __die
> page_fault_oops
> kernelmode_fixup_or_oops.constprop
> __bad_area_nosemaphore.constprop
> bad_area_nosemaphore
> do_user_addr_fault
> prb_read_valid
> exc_page_fault
> pvclock_clocksource_read_nowd
> handle_exception
> pvclock_clocksource_read_nowd
> __ring_buffer_alloc
> pvclock_clocksource_read_nowd
> __ring_buffer_alloc
> early_trace_init
> start_kernel
> i386_start_kernel
> startup_32_smp
> [...]
> ===
> I could transcribe all of it or capture it again from latest git and
> decode the symbols, if truely really needed, but I figured the type of
> crash and the trace itself could maybe be sufficient. It looks identical
> to me for all later crashing kernel versions.
> 
> I bisected this down to commit fbf6449f84bf5e4ad09f2c09ee70ed7d629b5ff6.
> 
> The kernel config [2] I used is 'make olddefconfig' based on Debian's
> config-6.8.11-686-pae [3].
> 
> I also tested 6.9.2 and 6.10-rc1, both also still crash in the same way.
> 
> cpuinfo:
> ===
> manx@caesar:~$ cat /proc/cpuinfo
> processor       : 0
> vendor_id       : AuthenticAMD
> cpu family      : 6
> model           : 8
> model name      : AMD Duron(tm)
> stepping        : 1
> cpu MHz         : 1798.331
> cache size      : 64 KB
> physical id     : 0
> siblings        : 1
> core id         : 0
> cpu cores       : 1
> apicid          : 0
> initial apicid  : 0
> fdiv_bug        : no
> f00f_bug        : no
> coma_bug        : no
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 1
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> mca cmov pat pse36 mmx fxsr sse syscall mmxext 3dnowext 3dnow cpuid
> 3dnowprefetch vmmcall
> bugs            : fxsave_leak sysret_ss_attrs spectre_v1 spectre_v2
> spec_store_bypass
> bogomips        : 3596.66
> clflush size    : 32
> cache_alignment : 32
> address sizes   : 34 bits physical, 32 bits virtual
> power management: ts
> ===
> 
> dmesg from a successful boot (Debian kernel 6.6.15-2) is here [4].
> 
> This particular system has been running all Debian testing kernels since
> at least the 2.6.32 days and is currently running 6.6.15-2 completely
> fine, thus this is an obvious regression.
> 
> The original Debian bug is #1071378 [5].
> 
> 
> #regzbot introduced: fbf6449f84bf5e4ad09f2c09ee70ed7d629b5ff6
> 
> [1] https://manx.datengang.de/temp/linux-6.7-crash/6.7.12-1-crash.png
> [2] https://manx.datengang.de/temp/linux-6.7-crash/config
> [3] https://manx.datengang.de/temp/linux-6.7-crash/config-6.8.11-686-pae
> [4] https://manx.datengang.de/temp/linux-6.7-crash/dmesg-6.6.15-2.txt
> [5] https://bugs.debian.org/1071378
> 
> 
> Best regards,
> Jörn
> 
>