linux-kernel - Re: [PATCH v2][EFI] Run EFI in physical mode

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Date:	Thu, 16 Dec 2010 12:22:14 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Takao Indoh <indou.takao@...fujitsu.com>
CC:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	horms@...ge.net.au, nhorman@...driver.com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, ebiederm@...ssion.com, tglx@...utronix.de,
	vgoyal@...hat.com
Subject: Re: [PATCH v2][EFI] Run EFI in physical mode

On 12/14/2010 10:01 AM, Takao Indoh wrote:
> On Tue, 14 Dec 2010 12:43:58 +0900, Kenji Kaneshige wrote:
> 
>> Hi,
>>
>> I tested this patch on the system that has large amount of memory (1TB),
>> and I encountered the immediate system reset problem that happens every
>> time I modify the EFI boot entry using efibootmgr command. It seems that
>> triple fault happens due to the incorrect page table setup.
>>
>>> +void __init efi_pagetable_init(void)
>>> +{
>> (snip.)
>>> +	pgd = efi_pgd + pgd_index(PAGE_OFFSET);
>>> +	set_pgd(pgd, *pgd_offset_k(PAGE_OFFSET));
>>> +	pgd = efi_pgd + pgd_index(__START_KERNEL_map);
>>> +	set_pgd(pgd, *pgd_offset_k(__START_KERNEL_map));
>>> +}
>>
>> Maybe we need to map whole kernel address space. The problem doesn't
>> happen by modifying as follows.
>>
>> 	clone_pgd_range(efi_pgd + KERNEL_PGD_BOUNDARY,
>> 			swapper_pg_dir + KERNEL_PGD_BOUNDARY, 
>> KERNEL_PGD_PTRS);
> 
> Agree, I'll merge this to the patch. And I got another bug report. This
> should be also merged.
> 
> 
> @@ -177,8 +177,8 @@ void __init efi_pagetable_init(void)
>  	memset(efi_pgd, 0, sizeof(efi_pgd));
>  	for (p = memmap.map; p < memmap.map_end; p += memmap.desc_size) {
>  		md = p;
> -		if (!(md->type & EFI_RUNTIME_SERVICES_CODE) &&
> -		    !(md->type & EFI_RUNTIME_SERVICES_DATA))
> +		if ((md->type != EFI_RUNTIME_SERVICES_CODE) &&
> +		    (md->type != EFI_RUNTIME_SERVICES_DATA))
>  			continue;
>  
>  		start_pfn = md->phys_addr >> PAGE_SHIFT;
> @@ -191,7 +191,7 @@ void __init efi_pagetable_init(void)
>  			pud = fill_pud(pgd, vaddr);
>  			pmd = fill_pmd(pud, vaddr);
>  			pte = fill_pte(pmd, vaddr);
> -			if (md->type & EFI_RUNTIME_SERVICES_CODE)
> +			if (md->type == EFI_RUNTIME_SERVICES_CODE)
>  				set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC));
>  			else
>  				set_pte(pte, pfn_pte(pfn, PAGE_KERNEL));
> 

Note: the current kernel has initial_page_table around for 32 bits; we
should do the equivalent for 64 bits and always keep a 1:1 page table
set around instead of having a special page table.  As such, I would
prefer to not merge a patchset that adds yet another set of ad hoc page
tables if at all possible.

	-hpa

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