[Crash-utility] Re: [PATCH 1/2] arm64: fix phys_offset for a negative memstart_addr

Since kernel commit 7bc1a0f9e176 ("arm64: mm: use single quantity to represent the PA to VA translation") memstart_addr is no longer always a physical address. For a 52-bit VA kernel that runs with fewer than 52 bits of VA, the kernel adjusts it by _PAGE_OFFSET(48) - _PAGE_OFFSET(52), which makes it negative. crash stored that value in phys_offset and used it as the physical base of the dumpfile, so a dumpfile from such a kernel failed during initialization: crash: seek error: kernel virtual address: ffff00003fde1c40 type: "memory section root table" Convert the negative value back to the real physical base before it is stored in phys_offset. Apply the conversion to every source of phys_offset: vmcoreinfo, the memstart_addr symbol, /proc/iomem, diskdump and kdump. Use the named ARM64_FLIP_PAGE_OFFSET_48 and ARM64_FLIP_PAGE_OFFSET_52 constants for the adjustment. This keeps live /proc/kcore debugging on 5.4-5.10 kernels working as well; that path still reads the kernel's physvirt_offset and uses it to correct phys_offset. Verified on a 7.3 arm64 dumpfile (4K pages, 52-bit VA configured, 48-bit VA active, KASLR) where PHYS_OFFSET is exported as 0xfff1000040000000 and the physical base is 0x40000000. Signed-off-by: Dave Young <yangrr.2009(a)tsinghua.org.cn&gt; --- arm64.c | 42 ++++++++++++++++++++++++++++++++++++------ defs.h | 7 +++++++ 2 files changed, 43 insertions(+), 6 deletions(-) diff --git a/arm64.c b/arm64.c index 654b9726cfe1..01b3bf783a8c 100644 --- a/arm64.c +++ b/arm64.c @@ -1719,7 +1719,11 @@ arm64_calc_physvirt_offset(void) machdep->flags |= HAS_PHYSVIRT_OFFSET; ms->physvirt_offset = physvirt_offset; - /* Update the ms->phys_offset which is wrong */ + /* + * physvirt_offset is authoritative on 5.4-5.10 + * kernels; reading it is what makes live + * /proc/kcore debugging work. + */ ms->phys_offset = ms->physvirt_offset + ms->page_offset; return; } @@ -1739,6 +1743,30 @@ arm64_calc_physvirt_offset(void) } +/* + * Store the kernel's "memstart_addr" value as the physical base address + * of the dumpfile. + * + * Since kernel commit 7bc1a0f9e176 ("arm64: mm: use single quantity to + * represent the PA to VA translation") memstart_addr is no longer always + * a physical address: for a 52-bit VA kernel running with less than 52 + * bits of VA, the kernel adjusts it by _PAGE_OFFSET(48) - _PAGE_OFFSET(52) + * so that it becomes negative. crash needs the real physical base for + * address translation. + */ +static void +arm64_store_phys_offset(ulong value) +{ + struct machine_specific *ms = machdep->machspec; + long memstart_addr = (long)value; + + if (memstart_addr < 0) + ms->phys_offset = memstart_addr + + ARM64_FLIP_PAGE_OFFSET_48 - ARM64_FLIP_PAGE_OFFSET_52; + else + ms->phys_offset = value; +} + static void arm64_calc_phys_offset(void) { @@ -1766,8 +1794,10 @@ arm64_calc_phys_offset(void) if ((machdep->flags & NEW_VMEMMAP) && ms->kimage_voffset && (sp = kernel_symbol_search("memstart_addr"))) { if (pc->flags & PROC_KCORE) { - if (arm64_get_vmcoreinfo(&ms->phys_offset, "NUMBER(PHYS_OFFSET)", NUM_HEX)) + if (arm64_get_vmcoreinfo(&phys_offset, "NUMBER(PHYS_OFFSET)", NUM_HEX)) { + arm64_store_phys_offset(phys_offset); return; + } vaddr = symbol_value_from_proc_kallsyms("memstart_addr"); if (vaddr == BADVAL) vaddr = sp->value; @@ -1778,7 +1808,7 @@ arm64_calc_phys_offset(void) } if (READMEM(pc->mfd, &phys_offset, sizeof(phys_offset), vaddr, paddr) > 0) { - ms->phys_offset = phys_offset; + arm64_store_phys_offset(phys_offset); return; } @@ -1813,11 +1843,11 @@ arm64_calc_phys_offset(void) if (errflag) return; - ms->phys_offset = phys_offset; + arm64_store_phys_offset(phys_offset); } else if (DISKDUMP_DUMPFILE() && diskdump_phys_base(&phys_offset)) { - ms->phys_offset = phys_offset; + arm64_store_phys_offset(phys_offset); } else if (KDUMP_DUMPFILE() && arm64_kdump_phys_base(&phys_offset)) { - ms->phys_offset = phys_offset; + arm64_store_phys_offset(phys_offset); } else { error(WARNING, "phys_offset cannot be determined from the dumpfile.\n"); diff --git a/defs.h b/defs.h index ad874e99c335..d05b3f34e2f4 100644 --- a/defs.h +++ b/defs.h @@ -3509,6 +3509,13 @@ typedef signed int s32; << (machdep->machspec->VA_BITS - 1)) /* kernels >= v5.4 the kernel VA space is flipped */ #define ARM64_FLIP_PAGE_OFFSET (-(1UL) << machdep->machspec->VA_BITS) +/* + * Fixed 48/52-bit page offsets, used to decode the kernel's negative + * memstart_addr when CONFIG_ARM64_VA_BITS_52 is enabled but fewer than + * 52 VA bits are active. + */ +#define ARM64_FLIP_PAGE_OFFSET_48 (-(1UL) << 48) +#define ARM64_FLIP_PAGE_OFFSET_52 (-(1UL) << 52) #define ARM64_USERSPACE_TOP ((1UL) << machdep->machspec->VA_BITS) #define ARM64_USERSPACE_TOP_ACTUAL ((1UL) << machdep->machspec->VA_BITS_ACTUAL)