With ARMv8.2-LVA architecture extension availability, arm64 hardware which supports this extension can support a virtual address-space upto 52-bits.
Since at the moment we enable the support of this extension in kernel via CONFIG flags, e.g. - User-space 52-bit LVA via CONFIG_ARM64_USER_VA_BITS_52 so, there is no clear mechanism in the user-space right now to determine these CONFIG flag values and hence determine the maximum virtual address space supported by the underlying kernel. User-space tools like 'makedumpfile' therefore are broken currently as they have no proper method to calculate the 'PTRS_PER_PGD' value which is required to perform a page table walk to determine the physical address of a corresponding virtual address found in kcore/vmcoreinfo. If one appends 'PTRS_PER_PGD' number to vmcoreinfo for arm64, it can be used in user-space to determine the maximum virtual address supported by underlying kernel. A reference 'makedumpfile' implementation which uses this approach to determining the maximum physical address is available in [0]. [0]. https://github.com/bhupesh-sharma/makedumpfile/blob/52-bit-va-support-via-vmcore-upstream-v3/arch/arm64.c#L459 Cc: Mark Rutland <[email protected]> Cc: Will Deacon <[email protected]> Cc: James Morse <[email protected]> Cc: Dave Anderson <[email protected]> Cc: Kazuhito Hagio <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Suggested-by: Steve Capper <[email protected]> Signed-off-by: Bhupesh Sharma <[email protected]> --- arch/arm64/kernel/crash_core.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm64/kernel/crash_core.c b/arch/arm64/kernel/crash_core.c index ca4c3e12d8c5..123a42c56b8e 100644 --- a/arch/arm64/kernel/crash_core.c +++ b/arch/arm64/kernel/crash_core.c @@ -10,6 +10,7 @@ void arch_crash_save_vmcoreinfo(void) { VMCOREINFO_NUMBER(VA_BITS); + VMCOREINFO_NUMBER(PTRS_PER_PGD); /* Please note VMCOREINFO_NUMBER() uses "%d", not "%x" */ vmcoreinfo_append_str("NUMBER(kimage_voffset)=0x%llx\n", kimage_voffset); -- 2.7.4
