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Message-ID: <20250417162206.GA104424@ax162>
Date: Thu, 17 Apr 2025 09:22:06 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>, Andy Shevchenko <andy@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Arnd Bergmann <arnd@...nel.org>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Davide Ciminaghi <ciminaghi@...dd.com>,
Ingo Molnar <mingo@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>,
"H. Peter Anvin" <hpa@...or.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/e820: discard high memory that can't be addressed by
32-bit systems
Hi Mike,
On Sun, Apr 13, 2025 at 11:08:58AM +0300, Mike Rapoport wrote:
...
> arch/x86/kernel/e820.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index 57120f0749cc..5f673bd6c7d7 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -1300,6 +1300,14 @@ void __init e820__memblock_setup(void)
> memblock_add(entry->addr, entry->size);
> }
>
> + /*
> + * 32-bit systems are limited to 4BG of memory even with HIGHMEM and
> + * to even less without it.
> + * Discard memory after max_pfn - the actual limit detected at runtime.
> + */
> + if (IS_ENABLED(CONFIG_X86_32))
> + memblock_remove(PFN_PHYS(max_pfn), -1);
> +
> /* Throw away partial pages: */
> memblock_trim_memory(PAGE_SIZE);
Our CI noticed a boot failure after this change as commit 1e07b9fad022
("x86/e820: Discard high memory that can't be addressed by 32-bit
systems") in -tip when booting i386_defconfig with a simple buildroot
initrd.
$ make -skj"$(nproc)" ARCH=i386 CROSS_COMPILE=i386-linux- mrproper defconfig bzImage
$ curl -LSs https://github.com/ClangBuiltLinux/boot-utils/releases/download/20241120-044434/x86-rootfs.cpio.zst | zstd -d >rootfs.cpio
$ qemu-system-i386 \
-display none \
-nodefaults \
-M q35 \
-d unimp,guest_errors \
-append 'console=ttyS0 earlycon=uart8250,io,0x3f8' \
-kernel arch/x86/boot/bzImage \
-initrd rootfs.cpio \
-cpu host \
-enable-kvm \
-m 512m \
-smp 8 \
-serial mon:stdio
[ 0.000000] Linux version 6.15.0-rc1-00177-g1e07b9fad022 (nathan@...62) (i386-linux-gcc (GCC) 14.2.0, GNU ld (GNU Binutils) 2.42) #1 SMP PREEMPT_DYNAMIC Thu Apr 17 09:02:19 MST 2025
[ 0.000000] BIOS-provided physical RAM map:
[ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
[ 0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
[ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x000000001ffdffff] usable
[ 0.000000] BIOS-e820: [mem 0x000000001ffe0000-0x000000001fffffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000b0000000-0x00000000bfffffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000fed1c000-0x00000000fed1ffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
[ 0.000000] earlycon: uart8250 at I/O port 0x3f8 (options '')
[ 0.000000] printk: legacy bootconsole [uart8250] enabled
[ 0.000000] Notice: NX (Execute Disable) protection cannot be enabled: non-PAE kernel!
[ 0.000000] APIC: Static calls initialized
[ 0.000000] SMBIOS 2.8 present.
[ 0.000000] DMI: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 0.000000] DMI: Memory slots populated: 1/1
[ 0.000000] Hypervisor detected: KVM
[ 0.000000] kvm-clock: Using msrs 4b564d01 and 4b564d00
[ 0.000000] kvm-clock: using sched offset of 196444860 cycles
[ 0.000589] clocksource: kvm-clock: mask: 0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
[ 0.002401] tsc: Detected 2750.000 MHz processor
[ 0.003126] last_pfn = 0x1ffe0 max_arch_pfn = 0x100000
[ 0.003728] MTRR map: 4 entries (3 fixed + 1 variable; max 19), built from 8 variable MTRRs
[ 0.004664] x86/PAT: Configuration [0-7]: WB WC UC- UC WB WP UC- WT
[ 0.007149] found SMP MP-table at [mem 0x000f5480-0x000f548f]
[ 0.007802] No sub-1M memory is available for the trampoline
[ 0.008435] Failed to release memory for alloc_low_pages()
[ 0.008438] RAMDISK: [mem 0x1fa5f000-0x1ffdffff]
[ 0.009571] Kernel panic - not syncing: Cannot find place for new RAMDISK of size 5771264
[ 0.010486] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.15.0-rc1-00177-g1e07b9fad022 #1 PREEMPT(undef)
[ 0.011601] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 0.012857] Call Trace:
[ 0.013135] dump_stack_lvl+0x43/0x58
[ 0.013555] dump_stack+0xd/0x10
[ 0.013919] panic+0xa5/0x221
[ 0.014252] setup_arch+0x86f/0x9f0
[ 0.014650] ? vprintk_default+0x29/0x30
[ 0.015089] start_kernel+0x4b/0x570
[ 0.015487] i386_start_kernel+0x65/0x68
[ 0.015919] startup_32_smp+0x151/0x154
[ 0.016344] ---[ end Kernel panic - not syncing: Cannot find place for new RAMDISK of size 5771264 ]---
At the parent change with the same command, the boot completes fine.
[ 0.000000] Linux version 6.15.0-rc1-00176-gd466304c4322 (nathan@...62) (i386-linux-gcc (GCC) 14.2.0, GNU ld (GNU Binutils) 2.42) #1 SMP PREEMPT_DYNAMIC Thu Apr 17 09:00:12 MST 2025
[ 0.000000] BIOS-provided physical RAM map:
...
[ 0.000000] earlycon: uart8250 at I/O port 0x3f8 (options '')
[ 0.000000] printk: legacy bootconsole [uart8250] enabled
[ 0.000000] Notice: NX (Execute Disable) protection cannot be enabled: non-PAE kernel!
[ 0.000000] APIC: Static calls initialized
[ 0.000000] SMBIOS 2.8 present.
[ 0.000000] DMI: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 0.000000] DMI: Memory slots populated: 1/1
[ 0.000000] Hypervisor detected: KVM
[ 0.000000] kvm-clock: Using msrs 4b564d01 and 4b564d00
[ 0.000001] kvm-clock: using sched offset of 429786443 cycles
[ 0.000806] clocksource: kvm-clock: mask: 0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
[ 0.003278] tsc: Detected 2750.000 MHz processor
[ 0.004730] last_pfn = 0x1ffe0 max_arch_pfn = 0x100000
[ 0.006220] MTRR map: 4 entries (3 fixed + 1 variable; max 19), built from 8 variable MTRRs
[ 0.009169] x86/PAT: Configuration [0-7]: WB WC UC- UC WB WP UC- WT
[ 0.012840] found SMP MP-table at [mem 0x000f5480-0x000f548f]
[ 0.014310] RAMDISK: [mem 0x1fa5f000-0x1ffdffff]
[ 0.015141] ACPI: Early table checksum verification disabled
...
[ 0.046564] 511MB LOWMEM available.
[ 0.047421] mapped low ram: 0 - 1ffe0000
[ 0.048431] low ram: 0 - 1ffe0000
[ 0.049289] Zone ranges:
[ 0.049934] DMA [mem 0x0000000000001000-0x0000000000ffffff]
[ 0.051184] Normal [mem 0x0000000001000000-0x000000001ffdffff]
[ 0.053087] Movable zone start for each node
[ 0.054409] Early memory node ranges
[ 0.055513] node 0: [mem 0x0000000000001000-0x000000000009efff]
[ 0.057411] node 0: [mem 0x0000000000100000-0x000000001ffdffff]
[ 0.059176] Initmem setup node 0 [mem 0x0000000000001000-0x000000001ffdffff]
...
Is this an invalid configuration or virtual setup that is being tested
here or is there something else problematic with this change?
Cheers,
Nathan
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