linux-kernel - Re: Qemu v9.0.2: Boot failed qemu-arm with Linux next-20241017 tag.

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Message-Id: <4730e562-7d14-4f12-897a-e23783d094af@app.fastmail.com>
Date: Wed, 23 Oct 2024 16:24:43 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Naresh Kamboju" <naresh.kamboju@...aro.org>,
 "open list" <linux-kernel@...r.kernel.org>,
 "Linux ARM" <linux-arm-kernel@...ts.infradead.org>,
 lkft-triage@...ts.linaro.org,
 "Linux Regressions" <regressions@...ts.linux.dev>, qemu-devel@...gnu.org
Cc: "Mark Brown" <broonie@...nel.org>,
 "Catalin Marinas" <catalin.marinas@....com>,
 "Aishwarya TCV" <Aishwarya.TCV@....com>,
 "Peter Maydell" <peter.maydell@...aro.org>,
 Alex Bennée <alex.bennee@...aro.org>,
 "Anders Roxell" <anders.roxell@...aro.org>,
 "Vincenzo Frascino" <vincenzo.frascino@....com>,
 "Thomas Gleixner" <tglx@...utronix.de>,
 "Geert Uytterhoeven" <geert@...ux-m68k.org>
Subject: Re: Qemu v9.0.2: Boot failed qemu-arm with Linux next-20241017 tag.

On Sun, Oct 20, 2024, at 17:39, Naresh Kamboju wrote:
> On Fri, 18 Oct 2024 at 12:35, Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
>>
>> The QEMU-ARMv7 boot has failed with the Linux next-20241017 tag.
>> The boot log is incomplete, and no kernel crash was detected.
>> However, the system did not proceed far enough to reach the login prompt.
>>

> Anders bisected this boot regressions and found,
> # first bad commit:
>   [efe8419ae78d65e83edc31aad74b605c12e7d60c]
>     vdso: Introduce vdso/page.h
>
> We are investigating the reason for boot failure due to this commit.

Anders and I did the analysis on this, the problem turned out
to be the early_init_dt_add_memory_arch() function in
drivers/of/fdt.c, which does bitwise operations on PAGE_MASK
with a 'u64' instead of phys_addr_t:

void __init __weak early_init_dt_add_memory_arch(u64 base, u64 size)
{
        const u64 phys_offset = MIN_MEMBLOCK_ADDR;

        if (size < PAGE_SIZE - (base & ~PAGE_MASK)) {
                pr_warn("Ignoring memory block 0x%llx - 0x%llx\n",
                        base, base + size);
                return;
        }

        if (!PAGE_ALIGNED(base)) {
                size -= PAGE_SIZE - (base & ~PAGE_MASK);
                base = PAGE_ALIGN(base);
        }

On non-LPAE arm32, this broke the existing behavior for
large 32-bit memory sizes. The obvious fix is to change
back the PAGE_MASK definition for 32-bit arm to a signed
number.

mips32, ppc32 and hexagon had the same definition as
well, so I think we should change at least those in order
to restore the previous behavior in case they are affected
by the same bug (or a different one).

x86-32 and arc git flipped the other way by the patch,
from unsigned to signed, when CONFIG_ARC_HAS_PAE40
or CONFIG_X86_PAE are set. I think we should keep
the 'signed' behavior as this was a bugfix by itself,
but we may want to change arc and x86-32 with short
phys_addr_t the same way for consistency.

On csky, m68k, microblaze, nios2, openrisc, parisc32,
riscv32, sh, sparc32, um and xtensa, we've always used
the 'unsigned' PAGE_MASK, and there is no 64-bit
phys_addr_t, so I would lean towards staying with
'unsigned' in order to not introduce a regression.
Alternatively we could choose to go with the 'signed'
version on all 32-bit architectures unconditionally
for consistency. Any preferences?

      Arnd