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Message-ID: <20241221002906.GA2558963@ax162>
Date: Fri, 20 Dec 2024 17:29:06 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Ard Biesheuvel <ardb@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Ryan Roberts <ryan.roberts@....com>,
Anshuman Khandual <anshuman.khandual@....com>,
Kees Cook <keescook@...omium.org>,
Quentin Perret <qperret@...gle.com>
Subject: Re: [PATCH v3 6/6] arm64/mm: Drop configurable 48-bit physical
address space limit
Hi Ard,
On Thu, Dec 12, 2024 at 09:18:48AM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
>
> Currently, the maximum supported physical address space can be
> configured as either 48 bits or 52 bits. The only remaining difference
> between these in practice is that the former omits the masking and
> shifting required to construct TTBR and PTE values, which carry bits #48
> and higher disjoint from the rest of the physical address.
>
> The overhead of performing these additional calculations is negligible,
> and so there is little reason to retain support for two different
> configurations, and we can simply support whatever the hardware
> supports.
I am seeing a boot failure after this change as commit 32d053d6f5e9
("arm64/mm: Drop configurable 48-bit physical address space limit") in
next-20241220 with several distribution configurations that all set
ARM64_VA_BITS_48. I can reproduce it on bare metal and in QEMU. Simply:
$ echo 'CONFIG_ARM64_VA_BITS_52=n
CONFIG_ARM64_VA_BITS_48=y' >kernel/configs/repro.config
$ make -skj"$(nproc)" ARCH=arm64 CROSS_COMPILE=aarch64-linux- mrproper defconfig repro.config Image.gz
$ git diff --no-index .config.old .config
diff --git a/.config.old b/.config
index c6dfbacfae06..371145bbe022 100644
--- a/.config.old
+++ b/.config
@@ -290,7 +290,7 @@ CONFIG_MMU=y
CONFIG_ARM64_CONT_PTE_SHIFT=4
CONFIG_ARM64_CONT_PMD_SHIFT=4
CONFIG_ARCH_MMAP_RND_BITS_MIN=18
-CONFIG_ARCH_MMAP_RND_BITS_MAX=18
+CONFIG_ARCH_MMAP_RND_BITS_MAX=33
CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN=11
CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX=16
CONFIG_STACKTRACE_SUPPORT=y
@@ -304,7 +304,7 @@ CONFIG_GENERIC_CALIBRATE_DELAY=y
CONFIG_SMP=y
CONFIG_KERNEL_MODE_NEON=y
CONFIG_FIX_EARLYCON_MEM=y
-CONFIG_PGTABLE_LEVELS=5
+CONFIG_PGTABLE_LEVELS=4
CONFIG_ARCH_SUPPORTS_UPROBES=y
CONFIG_ARCH_PROC_KCORE_TEXT=y
CONFIG_BUILTIN_RETURN_ADDRESS_STRIPS_PAC=y
@@ -426,7 +426,9 @@ CONFIG_ARM64_4K_PAGES=y
# CONFIG_ARM64_16K_PAGES is not set
# CONFIG_ARM64_64K_PAGES is not set
# CONFIG_ARM64_VA_BITS_39 is not set
-CONFIG_ARM64_VA_BITS=52
+CONFIG_ARM64_VA_BITS_48=y
+# CONFIG_ARM64_VA_BITS_52 is not set
+CONFIG_ARM64_VA_BITS=48
CONFIG_ARM64_LPA2=y
# CONFIG_CPU_BIG_ENDIAN is not set
CONFIG_CPU_LITTLE_ENDIAN=y
@@ -11259,6 +11261,3 @@ CONFIG_MEMTEST=y
#
# end of Rust hacking
# end of Kernel hacking
-
-CONFIG_ARM64_VA_BITS_52=n
-CONFIG_ARM64_VA_BITS_48=y
$ qemu-system-aarch64 --version | head -1
QEMU emulator version 9.2.0 (qemu-9.2.0-1.fc42)
# With TCG, there is a crash
$ qemu-system-aarch64 \
-display none \
-nodefaults \
-cpu max,pauth-impdef=true \
-machine virt,gic-version=max,virtualization=true \
-append 'console=ttyAMA0 earlycon' \
-kernel arch/arm64/boot/Image.gz \
-initrd rootfs.cpio \
-m 512m -serial mon:stdio
[ 0.000000] Booting Linux on physical CPU 0x0000000000 [0x000f0510]
[ 0.000000] Linux version 6.13.0-rc2-00006-g32d053d6f5e9 (nathan@...large-arm64) (aarch64-linux-gcc (GCC) 14.2.0, GNU ld (GNU Binutils) 2.42) #1 SMP PREEMPT Fri Dec 20 23:42:18 UTC 2024
...
[ 0.000000] Unable to handle kernel paging request at virtual address ffff80008001ffe8
[ 0.000000] Mem abort info:
[ 0.000000] ESR = 0x0000000096000004
[ 0.000000] EC = 0x25: DABT (current EL), IL = 32 bits
[ 0.000000] SET = 0, FnV = 0
[ 0.000000] EA = 0, S1PTW = 0
[ 0.000000] FSC = 0x04: level 0 translation fault
[ 0.000000] Data abort info:
[ 0.000000] ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
[ 0.000000] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 0.000000] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 0.000000] swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000041f10000
[ 0.000000] [ffff80008001ffe8] pgd=0000000000000000, p4d=0000000000000000, pud=1000000043017403, pmd=1000000043018403, pte=006800000800f713
[ 0.000000] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.13.0-rc2-00006-g32d053d6f5e9 #1
[ 0.000000] Hardware name: linux,dummy-virt (DT)
[ 0.000000] pstate: 800000c9 (Nzcv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 0.000000] pc : readl_relaxed+0x0/0x8
[ 0.000000] lr : gic_validate_dist_version+0x18/0x3c
[ 0.000000] sp : ffffb0df9bf63c90
[ 0.000000] x29: ffffb0df9bf63c90 x28: 0000000000000000 x27: 0000000000000000
[ 0.000000] x26: ffffb0df9bf63d78 x25: 0000000000000008 x24: dead000000000122
[ 0.000000] x23: ffff800080010000 x22: ffffb0df9bf63d88 x21: ffffb0df9bf63d78
[ 0.000000] x20: 0000000000000000 x19: ffff39131ff08a68 x18: 0000000000000001
[ 0.000000] x17: 0000000000000068 x16: 0000000000000100 x15: ffffb0df9b722ee0
[ 0.000000] x14: 0000000000000000 x13: ffff800080021000 x12: ffff80008001ffff
[ 0.000000] x11: 0000000000000000 x10: 0000000008010000 x9 : 0000000008010000
[ 0.000000] x8 : ffff80008001ffff x7 : ffff391303017008 x6 : ffff800080020000
[ 0.000000] x5 : 000000000000003f x4 : 000000000000003f x3 : 0000000000000000
[ 0.000000] x2 : 0000000000000000 x1 : 000000000000ffe8 x0 : ffff80008001ffe8
[ 0.000000] Call trace:
[ 0.000000] readl_relaxed+0x0/0x8 (P)
[ 0.000000] gic_validate_dist_version+0x18/0x3c (L)
[ 0.000000] gic_of_init+0x98/0x278
[ 0.000000] of_irq_init+0x1d4/0x34c
[ 0.000000] irqchip_init+0x18/0x40
[ 0.000000] init_IRQ+0x9c/0xb4
[ 0.000000] start_kernel+0x528/0x6d4
[ 0.000000] __primary_switched+0x88/0x90
[ 0.000000] Code: a8c17bfd d50323bf d65f03c0 d503201f (b9400000)
[ 0.000000] ---[ end trace 0000000000000000 ]---
[ 0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
[ 0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
# Using KVM, there is just a hang
$ qemu-system-aarch64 \
-display none \
-nodefaults \
-machine virt,gic-version=max \
-append 'console=ttyAMA0 earlycon' \
-kernel arch/arm64/boot/Image.gz \
-initrd rootfs.cpio \
-cpu host \
-enable-kvm \
-m 512m \
-smp 8 \
-serial mon:stdio
Is this a configuration issue? Reverting this change makes everything
work again.
Cheers,
Nathan
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