Date: Sat, 13 Dec 2014 11:48:27 +0000
From: Matt Fleming <matt@console-pimps.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@linux.intel.com>,
        Ross Zwisler <ross.zwisler@linux.intel.com>,
        lttng-dev <lttng-dev@lists.lttng.org>, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andi Kleen <andi@firstfloor.org>, linux-efi@vger.kernel.org,
        Tony Luck <tony.luck@gmail.com>
Subject: Re: Progress on system crash traces with LTTng using DAX and pmem
Message-ID: <20141213114827.GA7761@console-pimps.org>
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On Thu, 30 Oct, at 03:11:36PM, Mathieu Desnoyers wrote:
> 
> Hi Kirill,
> 
> This is a good point,
> 
> There are a few more aspects to consider here:
> 
> - Other architectures appear to have different guarantees, for
>   instance ARM which, AFAIK, does not reset memory on soft
>   reboot (well at least for my customer's boards). So I guess
>   if x86 wants to be competitive, it would be good for them to
>   offer a similar feature,
> 
> - Already having a subset of machines supporting this is useful,
>   e.g. storing trace buffers and recovering them after a crash,
> 
> - Since we are in a world of dynamically upgradable BIOS, perhaps
>   if we can show that there is value in having a BIOS option to
>   specify a memory range that should not be reset on soft reboot,
>   BIOS vendors might be inclined to include an option for it,
> 
> - Perhaps UEFI BIOS already have some way of specifying that a
>   memory range should not be reset on soft reboot ?

We've achieved this in the past using UEFI capsules with the
EFI_CAPSULE_PERSIST_ACROSS_RESET header flag.

Unfortunately, runtime capsule support is pretty spotty, so it's not a
general solution right now.

-- 
Matt Fleming, Intel Open Source Technology Center
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