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From: Dave Young <dyoung@redhat.com>
To: Bhupesh Sharma <bhsharma@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Kazuhito Hagio <k-hagio@ab.jp.nec.com>,
	lijiang@redhat.com, bhe@redhat.com, ard.biesheuvel@linaro.org,
	catalin.marinas@arm.com, kexec@lists.infradead.org,
	Will Deacon <will.deacon@arm.com>,
	AKASHI Takahiro <takahiro.akashi@linaro.org>,
	James Morse <james.morse@arm.com>, Borislav Petkov <bp@alien8.de>,
	anderson@redhat.com, bhupesh.linux@gmail.com,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64, vmcoreinfo : Append 'MAX_USER_VA_BITS' and 'MAX_PHYSMEM_BITS' to vmcoreinfo
Date: Thu, 31 Jan 2019 09:48:00 +0800
Message-ID: <20190131014800.GB15785@dhcp-128-65.nay.redhat.com> (raw)
In-Reply-To: <1548850991-11879-1-git-send-email-bhsharma@redhat.com>

+ more people
On 01/30/19 at 05:53pm, Bhupesh Sharma wrote:
> With ARMv8.2-LVA and LPA architecture extensions, arm64 hardware which
> supports these extensions can support upto 52-bit virtual and 52-bit
> physical addresses respectively.
> 
> Since at the moment we enable the support of these extensions via CONFIG
> flags, e.g.
>  - LPA via CONFIG_ARM64_PA_BITS_52
> 
> there are no clear mechanisms in user-space right now to
> deteremine these CONFIG flag values and also determine the PARange and
> VARange address values.
> 
> User-space tools like 'makedumpfile' and 'crash-utility' can instead
> use the 'MAX_USER_VA_BITS' and 'MAX_PHYSMEM_BITS' values to determine
> the maximum virtual address and physical address (respectively)
> 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-pa-support-via-vmcore-v1/arch/arm64.c#L490

I'm not objecting the patch, just want to make sure to make clear about
things and make sure these issues are aware by people, and leave arm
people to review the arm bits.

1. MAX_PHYSMEM_BITS
As we previously found, back to 2014 makedumpfile took a patch to read the
value from vmcore but the kernel patch was not accepted.
So we should first make clear if this is really needed, why other arches
do not need this in makedumpfile.

If we really need it then should it be arm64 only?

If it is arm64 only then the makedumpfile code should read this number
only for arm64.

Also Lianbo added the vmcoreinfo documents, I believe it stays in -tip
tree,  need to make sure to document this as well.

2. MAX_USER_VA_BITS
Does makedumpfile care about userspace VA bits?  I do not see other code
doing this,  Kazu and Dave A should be able to comment.

I tend to doubt about this.

> 
> Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>
> ---
>  arch/arm64/kernel/crash_core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kernel/crash_core.c b/arch/arm64/kernel/crash_core.c
> index ca4c3e12d8c5..ad231be5c0d8 100644
> --- a/arch/arm64/kernel/crash_core.c
> +++ b/arch/arm64/kernel/crash_core.c
> @@ -10,6 +10,8 @@
>  void arch_crash_save_vmcoreinfo(void)
>  {
>  	VMCOREINFO_NUMBER(VA_BITS);
> +	VMCOREINFO_NUMBER(MAX_USER_VA_BITS);
> +	VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
>  	/* Please note VMCOREINFO_NUMBER() uses "%d", not "%x" */
>  	vmcoreinfo_append_str("NUMBER(kimage_voffset)=0x%llx\n",
>  						kimage_voffset);
> -- 
> 2.7.4
> 
> 
> _______________________________________________
> kexec mailing list
> kexec@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec

Thanks
Dave

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  parent reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-30 12:23 Bhupesh Sharma
2019-01-30 15:21 ` James Morse
2019-01-30 21:39   ` Bhupesh Sharma
2019-02-04 14:35     ` Bhupesh Sharma
2019-02-04 15:31       ` Robin Murphy
2019-02-12  4:55         ` Bhupesh Sharma
2019-02-12 10:49           ` Robin Murphy
2019-02-04 16:56       ` James Morse
2019-01-31  1:48 ` Dave Young [this message]
2019-01-31 10:00   ` Bhupesh Sharma
2019-01-31 14:03   ` Dave Anderson
2019-02-04 16:04   ` Kazuhito Hagio
2019-02-12  5:07     ` Bhupesh Sharma
2019-02-12 10:44       ` Dave Young
2019-02-12 19:59         ` Bhupesh Sharma
2019-02-12 23:03           ` Kazuhito Hagio
2019-02-13 11:15             ` Dave Young
2019-02-13 18:22               ` James Morse
2019-02-13 19:52                 ` Kazuhito Hagio
2019-02-15 17:34                   ` James Morse
2019-02-15 18:01                     ` Bhupesh Sharma
2019-02-18 15:27                       ` Steve Capper
2019-02-21 16:08                         ` Bhupesh Sharma
2019-02-19 20:47                       ` Kazuhito Hagio
2019-02-21 16:20                         ` Bhupesh Sharma
2019-02-21 16:42                           ` Dave Anderson
2019-02-21 19:02                             ` Kazuhito Hagio
2019-03-01  4:01                               ` Bhupesh Sharma
2019-02-14 19:30                 ` Bhupesh Sharma

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