Subject: [PATCH v3 5/6] ARM: mm: Recreate kernel mappings in early_paging_init()

From: [email-masked] (Santosh Shilimkar)
Date: Fri, 4 Oct 2013 12:12:36 -0400

On Friday 04 October 2013 11:59 AM, Will Deacon wrote:
> On Thu, Oct 03, 2013 at 10:17:59PM +0100, Santosh Shilimkar wrote:
>> This patch adds a step in the init sequence, in order to recreate
>> the kernel code/data page table mappings prior to full paging
>> initialization.  This is necessary on LPAE systems that run out of
>> a physical address space outside the 4G limit.  On these systems,
>> this implementation provides a machine descriptor hook that allows
>> the PHYS_OFFSET to be overridden in a machine specific fashion.
> 
> [...]
> 
>> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
>> index b1d17ee..47c7497 100644
>> --- a/arch/arm/mm/mmu.c
>> +++ b/arch/arm/mm/mmu.c
>> @@ -28,6 +28,7 @@
>>  #include <asm/highmem.h>
>>  #include <asm/system_info.h>
>>  #include <asm/traps.h>
>> +#include <asm/procinfo.h>
>>  
>>  #include <asm/mach/arch.h>
>>  #include <asm/mach/map.h>
>> @@ -1315,6 +1316,87 @@ static void __init map_lowmem(void)
>>  	}
>>  }
>>  
>> +#ifdef CONFIG_ARM_LPAE
>> +extern void fixup_pv_table(const void *, unsigned long);
>> +extern const void *__pv_table_begin, *__pv_table_end;
>> +
>> +/*
>> + * early_paging_init() recreates boot time page table setup, allowing machines
>> + * to switch over to a high (>4G) address space on LPAE systems
>> + */
>> +void __init early_paging_init(const struct machine_desc *mdesc,
>> +			      struct proc_info_list *procinfo)
>> +{
>> +	pmdval_t pmdprot = procinfo->__cpu_mm_mmu_flags;
>> +	unsigned long map_start, map_end;
>> +	pgd_t *pgd0, *pgdk;
>> +	pud_t *pud0, *pudk;
>> +	pmd_t *pmd0, *pmdk;
>> +	phys_addr_t phys;
>> +	int i;
>> +
>> +	/* remap kernel code and data */
>> +	map_start = init_mm.start_code;
>> +	map_end   = init_mm.brk;
>> +
>> +	/* get a handle on things... */
>> +	pgd0 = pgd_offset_k(0);
>> +	pud0 = pud_offset(pgd0, 0);
>> +	pmd0 = pmd_offset(pud0, 0);
>> +
>> +	pgdk = pgd_offset_k(map_start);
>> +	pudk = pud_offset(pgdk, map_start);
>> +	pmdk = pmd_offset(pudk, map_start);
>> +
>> +	phys = PHYS_OFFSET;
>> +
>> +	if (mdesc->init_meminfo) {
>> +		mdesc->init_meminfo();
>> +		/* Run the patch stub to update the constants */
>> +		fixup_pv_table(&__pv_table_begin,
>> +			(&__pv_table_end - &__pv_table_begin) << 2);
>> +
>> +		/*
>> +		 * Cache cleaning operations for self-modifying code
>> +		 * We should clean the entries by MVA but running a
>> +		 * for loop over every pv_table entry pointer would
>> +		 * just complicate the code.
>> +		 */
>> +		flush_cache_louis();
>> +		dsb();
>> +		isb();
> 
> You don't need either of these barriers.
> 
Agree. Just want to be clear, its because they are already present
in flush_cache_louis(), right ?

>> +	}
>> +
>> +	/* remap level 1 table */
>> +	for (i = 0; i < PTRS_PER_PGD; i++) {
>> +		*pud0++ = __pud(__pa(pmd0) | PMD_TYPE_TABLE | L_PGD_SWAPPER);
>> +		pmd0 += PTRS_PER_PMD;
>> +	}
>> +
>> +	/* remap pmds for kernel mapping */
>> +	phys = __pa(map_start) & PMD_MASK;
>> +	do {
>> +		*pmdk++ = __pmd(phys | pmdprot);
>> +		phys += PMD_SIZE;
>> +	} while (phys < map_end);
>> +
>> +	flush_cache_all();
> 
> Why are you being so heavyweight with your cacheflushing? If you're just
> interested in flushing the new page tables, then use the proper accessors to
> build them. The only case I think you need to flush the world is for VIVT,
> which you won't have with LPAE (you could have a BUG_ON here).
> 
It was mainly to avoid all the looping MVA based stuff but you have valid point.
I shall look at it and see what can be done.

>> +	cpu_set_ttbr(0, __pa(pgd0));
>> +	cpu_set_ttbr(1, __pa(pgd0) + TTBR1_OFFSET);
> 
> Can you not use cpu_switch_mm with the init_mm for this?
> 
Probably yes. Will have a look at it.

Regards,
Santosh