Messages in this thread Patch in this message | | | Date | Wed, 04 Aug 2010 16:05:47 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 1/2] x86-32: Fix crashes with CPU hotplug on AMD machines |
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On 08/04/2010 09:45 AM, Borislav Petkov wrote: > > 2. Do not use swapper_pg_dir to boot secondary CPUs like 64-bit > does. > > This patch implements solution 2. It introduces a trampoline_pg_dir > which has the same layout as swapper_pg_dir with low_mappings. This page > table is used as the initial page table of the booting CPU. Later in the > bringup process, it switches to swapper_pg_dir and does a global TLB > flush. This fixes the crashes in our test cases. >
I would like to keep around a page directory with the low mappings around -- and not use it for kernel threads -- at all times *anyway*. This means we can remove any current hacks that we have to do around S3 entry and exit, for example.
--- a/arch/x86/kernel/head_32.S +++ b/arch/x86/kernel/head_32.S @@ -328,7 +328,7 @@ ENTRY(startup_32_smp) /* * Enable paging */ - movl $pa(swapper_pg_dir),%eax + movl pa(initial_page_table), %eax movl %eax,%cr3 /* set the page table pointer.. */ movl %cr0,%eax orl $X86_CR0_PG,%eax @@ -608,6 +608,8 @@ ignore_int: .align 4 ENTRY(initial_code) .long i386_start_kernel +ENTRY(initial_page_table) + .long pa(swapper_pg_dir)
/* * BSS section @@ -623,6 +625,10 @@ ENTRY(swapper_pg_dir) #endif swapper_pg_fixmap: .fill 1024,4,0 +#ifdef CONFIG_X86_TRAMPOLINE +ENTRY(trampoline_pg_dir) + .fill 1024,4,0 +#endif
I don't really see why this makes sense, though. It would make more sense that the initial page table we set up becomes trampoline_pg_dir; we can then set up and change to swapper_pg_dir almost immediately.
I realize this isn't how the 64-bit code works at the moment, but in a lot of ways I think it would be better if it did.
-hpa
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