Re: [RESEND PATCH v5 1/5] crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS' to vmcoreinfo

From: John Donnelly <John.P.Donnelly@Oracle.com>
To: kexec@lists.infradead.org
Subject: Re: [RESEND PATCH v5 1/5] crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS' to vmcoreinfo
Date: Mon, 2 Dec 2019 17:55:12 -0600	[thread overview]
Message-ID: <07946b28-3855-f8e9-52bb-b5452758a18c@Oracle.com> (raw)
In-Reply-To: <1575057559-25496-2-git-send-email-bhsharma@redhat.com>

On 11/29/19 1:59 PM, Bhupesh Sharma wrote:
> Right now user-space tools like 'makedumpfile' and 'crash' need to rely
> on a best-guess method of determining value of 'MAX_PHYSMEM_BITS'
> supported by underlying kernel.
> 
> This value is used in user-space code to calculate the bit-space
> required to store a section for SPARESMEM (similar to the existing
> calculation method used in the kernel implementation):
> 
>    #define SECTIONS_SHIFT    (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
> 
> Now, regressions have been reported in user-space utilities
> like 'makedumpfile' and 'crash' on arm64, with the recently added
> kernel support for 52-bit physical address space, as there is
> no clear method of determining this value in user-space
> (other than reading kernel CONFIG flags).
> 
> As per suggestion from makedumpfile maintainer (Kazu), it makes more
> sense to append 'MAX_PHYSMEM_BITS' to vmcoreinfo in the core code itself
> rather than in arch-specific code, so that the user-space code for other
> archs can also benefit from this addition to the vmcoreinfo and use it
> as a standard way of determining 'SECTIONS_SHIFT' value in user-land.
> 
> A reference 'makedumpfile' implementation which reads the
> 'MAX_PHYSMEM_BITS' value from vmcoreinfo in a arch-independent fashion
> is available here:
> 
> [0]. https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_bhupesh-2Dsharma_makedumpfile_blob_remove-2Dmax-2Dphys-2Dmem-2Dbit-2Dv1_arch_ppc64.c-23L471&d=DwICAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=t2fPg9D87F7D8jm0_3CG9yoiIKdRg4qc_thBw4bzMhc&m=WdAKu3i_AeChZ2ZngChACvP5LtULN6mgHopxlQbu16Q&s=AYn-OBh6EqC80XVBg3oLc8ivaCwCNs-cm0PMkJ_2fjo&e=
> 
> Cc: Boris Petkov <bp@alien8.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: James Morse <james.morse@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Steve Capper <steve.capper@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Dave Anderson <anderson@redhat.com>
> Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
> Cc: x86@kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Cc: kexec@lists.infradead.org
> Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>

Tested-by:  John Donnelly <john.p.donnelly@oracle.com>

> ---
>   kernel/crash_core.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 9f1557b98468..18175687133a 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -413,6 +413,7 @@ static int __init crash_save_vmcoreinfo_init(void)
>   	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
>   	VMCOREINFO_STRUCT_SIZE(mem_section);
>   	VMCOREINFO_OFFSET(mem_section, section_mem_map);
> +	VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
>   #endif
>   	VMCOREINFO_STRUCT_SIZE(page);
>   	VMCOREINFO_STRUCT_SIZE(pglist_data);
> 


-- 
Thank You,
John

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