Messages in this thread Patch in this message | | | From | Bhupesh Sharma <> | Subject | [PATCH v3 1/3] arm64, vmcoreinfo : Append 'PTRS_PER_PGD' to vmcoreinfo | Date | Wed, 20 Mar 2019 10:39:32 +0530 |
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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 <mark.rutland@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Dave Anderson <anderson@redhat.com> Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com> Cc: linux-kernel@vger.kernel.org Cc: kexec@lists.infradead.org Cc: linux-arm-kernel@lists.infradead.org Suggested-by: Steve Capper <Steve.Capper@arm.com> Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com> --- 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
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