Messages in this thread | | | Subject | Re: [Fastboot] [PATCH] Reserving backup region for kexec based crashdumps. | From | (Eric W. Biederman) | Date | 03 Feb 2005 03:07:58 -0700 |
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Hirokazu Takahashi <taka@valinux.co.jp> writes:
> Hi Vivek, > > > > Hi Vivek and Eric, > > > > > > IMHO, why don't we swap not only the contents of the top 640K > > > but also kernel working memory for kdump kernel? > > > > > > Initial patches of kdump had adopted the same approach but given the > > fact devices are not stopped during transition to new kernel after a > > panic, it carried inherent risk of some DMA going on and corrupting the > > new kernel/data structures. Hence the idea of running the kernel from a > > reserved location came up. This should be DMA safe as long as DMA is not > > misdirected. > > I see, that makes sense. > But I'm not sure yet that it's safe to access the top of 640MB. 640K?
> I wonder how kmalloc(GFP_DMA) works in a kdump kernel.
All that happens there is a one line change to vmlinux.lds.S that causes the kernel to live at a different physical and virtual address. So everything works as normal.
I do agree that it is risky to use the first 640K for normal work. But on the list of things to fix it is a minor war, and even if we back up that region of memory we don't need to use it.
There are still remain a lot of code reviews to ensure the code is generally safe.
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