On 01/18/2013 05:05 PM, Mitch Bradley wrote: > > > On 1/18/2013 2:42 PM, H. Peter Anvin wrote: >> On 01/18/2013 04:40 PM, Andres Salomon wrote: >>> Bad news on this patch; I've been told that it breaks booting on an >>> XO-1.5. Does anyone from OLPC know why yet? >> >> What are the settings of CR0 and CR4 on kernel entry on XO-1.5? > > > CR0 is 0x80000011 > CR4 is 0x10 >
OK, that makes sense... the kernel doesn't enable the PSE bit yet and I bet that's what you're using for the non-stolen page tables. Can we simply disable paging before mucking with CR4? The other option that I can see is to always enable PSE and PGE, since they are simply features opt-ins that don't do any harm if unused. At the same time, though, entering the kernel through the default_entry path with paging enabled is definitely not anything the kernel expects. Does this patch work for you? Since we have ditched 386 support, we can mimic x86-64 (yay, one more difference gone!) and just use a predefined value for %cr0 (the FPU flags need to change if we are on an FPU-less chip, but that happens during FPU probing.) Does this patch work for you? -hpa
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S index 8e7f655..2713ea1 100644 --- a/arch/x86/kernel/head_32.S +++ b/arch/x86/kernel/head_32.S @@ -300,6 +300,11 @@ ENTRY(startup_32_smp) leal -__PAGE_OFFSET(%ecx),%esp default_entry: +#define CR0_STATE (X86_CR0_PE | X86_CR0_MP | X86_CR0_ET | \ + X86_CR0_NE | X86_CR0_WP | X86_CR0_AM | \ + X86_CR0_PG) + movl $(CR0_STATE & ~X86_CR0_PG),%eax + movl %eax,%cr0 /* * New page tables may be in 4Mbyte page mode and may * be using the global pages. @@ -364,8 +369,7 @@ default_entry: */ movl $pa(initial_page_table), %eax movl %eax,%cr3 /* set the page table pointer.. */ - movl %cr0,%eax - orl $X86_CR0_PG,%eax + movl $CR0_STATE,%eax movl %eax,%cr0 /* ..and set paging (PG) bit */ ljmp $__BOOT_CS,$1f /* Clear prefetch and normalize %eip */ 1: