Re: [PATCH 0/4] memblock related fixes for -tip

[Jeremy Fitzhardinge <jeremy@goop.org>]

 On 10/13/2010 04:18 PM, H. Peter Anvin wrote:
> On 10/13/2010 04:14 PM, Jeremy Fitzhardinge wrote:
>> The Xen code is setting the max_pfn_mapped correctly, but it is just
>> being overridden by:
>>
>> 	max_pfn_mapped = KERNEL_IMAGE_SIZE >> PAGE_SHIFT;
>>
>> in setup_arch() - and KERNEL_IMAGE_SIZE is hard-coded to 512MB...
>>
>> How is this correct?  Does kernel/head_64.S map everything up to 512MB
>> or something?
>>
> Yes:
>         /*
>          * 512 MB kernel mapping. We spend a full page on this pagetable
>          * anyway.
>          *
>          * The kernel code+data+bss must not be bigger than that.
>          *
>          * (NOTE: at +512MB starts the module area, see MODULES_VADDR.
>          *  If you want to increase this then increase MODULES_VADDR
>          *  too.)
>          */
>         PMDS(0, __PAGE_KERNEL_LARGE_EXEC,
>                 KERNEL_IMAGE_SIZE/PMD_SIZE)
>
> This is, however, wrong in the sense that it obviously shouldn't be
> getting executed on the Xen codepath.

I see.  head_32.S sets max_pfn_mapped for itself, so head_64.S should
probably do that too.  Patch below, but I haven't checked to see if it
fixes the original problem (but I don't see why the pagetable memory
allocation should be limited to the mapped region, especially if you
want to put it as high as possible, especially since the mm/init_64.c
code doesn't expect it to be mapped).

    J

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Date: Wed, 13 Oct 2010 16:31:11 -0700
Subject: [PATCH] x86-64: don't force max_pfn_mapped to 512MB

head_64.S maps up to 512MB, but the Xen entry path doesn't necessarily
map that high.  Set max_pfn_mapped in head_64.S accordingly.  (The Xen
code already sets max_pfn_mapped correctly.)

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 239046b..b75c6f4 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -141,6 +141,8 @@ ident_complete:
 	addq	%rbp, trampoline_level4_pgt + (511*8)(%rip)
 #endif
 
+	movq    $KERNEL_IMAGE_SIZE / PAGE_SIZE, max_pfn_mapped(%rip)
+
 	/* Due to ENTRY(), sometimes the empty space gets filled with
 	 * zeros. Better take a jmp than relying on empty space being
 	 * filled with 0x90 (nop)
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index b11a238..c3cebfe 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -932,7 +932,6 @@ void __init setup_arch(char **cmdline_p)
 		max_low_pfn = max_pfn;
 
 	high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
-	max_pfn_mapped = KERNEL_IMAGE_SIZE >> PAGE_SHIFT;
 #endif
 
 	/*