Messages in this thread | | | Date | Tue, 2 May 2006 10:35:18 +0900 | From | "Magnus Damm" <> | Subject | Re: [Fastboot] [PATCH] kexec: Avoid overwriting the current pgd (i386) |
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On 5/1/06, Vivek Goyal <vgoyal@in.ibm.com> wrote: > On Mon, May 01, 2006 at 06:49:16PM +0900, Magnus Damm wrote: > > kexec: Avoid overwriting the current pgd (i386) > > > > This patch upgrades the i386-specific kexec code to avoid overwriting the > > current pgd. Overwriting the current pgd is bad when CONFIG_CRASH_DUMP is used > > to start a secondary kernel that dumps the memory of the previous kernel. > > > > The code introduces a new set of page tables called "page_table_a". These > > tables are used to provide an executable identity mapping without overwriting > > the current pgd. > > True, current pgd is overwritten but that effects only user space mappings > and currently "crash" supports only backtracing kernel space code. But at > the same time probably it is not a bad idea to maintain a separate page > table and switch to that instead of overwriting the existing pgd. This > shall help if in future user space backtracing is also supported.
I agree, but I also think that overwriting user space mappings is bad from the trace perspective too, especially if you look at kernel data. I would say that user space page tables are just another kernel data structure, and overwriting them may result in things like inconsistent page->mapcount values.
Thanks for the comments,
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