Re: [PATCH] arm64/mm: Introduce a variable to hold base address of linear region

From: James Morse <james.morse@arm.com>
To: Bhupesh Sharma <bhsharma@redhat.com>,
	"Jin, Yanjiang" <yanjiang.jin@hxt-semitech.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	kexec <kexec-bounces@lists.infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	AKASHI Takahiro <takahiro.akashi@linaro.org>,
	Bhupesh SHARMA <bhupesh.linux@gmail.com>,
	Kexec Mailing List <kexec@lists.infradead.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] arm64/mm: Introduce a variable to hold base address of linear region
Date: Wed, 20 Jun 2018 11:06:33 +0100	[thread overview]
Message-ID: <aa9e1422-abbd-6d43-0a9f-eaf3476328a1@arm.com> (raw)
In-Reply-To: <CACi5LpMXpSWUP97R2VWjf==LdxPBCKTcpKjQjCs4j3Kz9SzYGg@mail.gmail.com>

Hi guys,

On 20/06/18 08:26, Bhupesh Sharma wrote:
> On Wed, Jun 20, 2018 at 7:46 AM, Jin, Yanjiang
> <yanjiang.jin@hxt-semitech.com> wrote:
>> If /proc/kcore always exists in kexec/kdump, I think this issue can be fixed
>> easily. But it requires  that Kexec/kdump have to rely on " CONFIG_PROC_KCORE=y".
>> I am not sure if we can persuade Kexec-tools community to accept this.

For the kernel this would be:
--------------%<--------------

diff --git a/arch/Kconfig b/arch/Kconfig
index 1aa59063f1fd..0ea2c7c0ac08 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -8,6 +8,7 @@ config CRASH_CORE

 config KEXEC_CORE
        select CRASH_CORE
+       select PROC_KCORE
        bool

 config HAVE_IMA_KEXEC
--------------%<--------------

With this kernel's that support kdump but don't have /proc/kcore wouldn't have
the new PT_NOTEs anyway. Whatever you do today is all you can do.


> Most distributions like Ubuntu and Fedora already enable
> CONFIG_PROC_KCORE by default, to support user-space tools like
> crash-utility and makedumpfile which can be used for 'live' debugging
> of a primary kernel (without the requirement of being in the secondary
> or crash kernel).
> 
> For such cases. '/proc/kcore' and 'vmlinux' are the only available
> sources for PT_NOTE/PT_LOAD segments and kernel symbols respectively.
> 
> Since we need to support all such existing user-space utilities (which
> work well with other archs like x86 and ppc64),

x86 has kaslr too, I couldn't work out how your user-space:phys_to_virt() works
there. Are we missing an alternative trick?


> we need to have a
> solution which works without modifying most of them - the rest (like
> kexec-tools) can be easily modified to follow the same approach.

(We're  also trying to solve this in a way that lets user-space shed
arch-specific code.)


Thanks,

James

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec
