Commit ee4f2ea4 authored by Benjamin Herrenschmidt's avatar Benjamin Herrenschmidt Committed by Paul Mackerras
Browse files

[POWERPC] Fix 32-bit mm operations when not using BATs 



On hash table based 32 bits powerpc's, the hash management code runs with
a big spinlock. It's thus important that it never causes itself a hash
fault. That code is generally safe (it does memory accesses in real mode
among other things) with the exception of the actual access to the code
itself. That is, the kernel text needs to be accessible without taking
a hash miss exceptions.

This is currently guaranteed by having a BAT register mapping part of the
linear mapping permanently, which includes the kernel text. But this is
not true if using the "nobats" kernel command line option (which can be
useful for debugging) and will not be true when using DEBUG_PAGEALLOC
implemented in a subsequent patch.

This patch fixes this by pre-faulting in the hash table pages that hit
the kernel text, and making sure we never evict such a page under hash
pressure.

Signed-off-by: default avatarBenjamin Herrenchmidt <benh@kernel.crashing.org>

 arch/powerpc/mm/hash_low_32.S |   22 ++++++++++++++++++++--
 arch/powerpc/mm/mem.c         |    3 ---
 arch/powerpc/mm/mmu_decl.h    |    4 ++++
 arch/powerpc/mm/pgtable_32.c  |   11 +++++++----
 4 files changed, 31 insertions(+), 9 deletions(-)
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent 3be4e699

arch/powerpc/mm/hash_low_32.S

+20 −2
Original line number Diff line number Diff line
@@ -283,6 +283,7 @@ Hash_msk = (((1 << Hash_bits) - 1) * 64) 
#define PTEG_SIZE	64

#define LG_PTEG_SIZE	6

#define LDPTEu		lwzu

#define LDPTE		lwz

#define STPTE		stw

#define CMPPTE		cmpw

#define PTE_H		0x40
@@ -389,13 +390,30 @@ _GLOBAL(hash_page_patch_C) 
	 * and we know there is a definite (although small) speed

	 * advantage to putting the PTE in the primary PTEG, we always

	 * put the PTE in the primary PTEG.

	 *

	 * In addition, we skip any slot that is mapping kernel text in

	 * order to avoid a deadlock when not using BAT mappings if

	 * trying to hash in the kernel hash code itself after it has

	 * already taken the hash table lock. This works in conjunction

	 * with pre-faulting of the kernel text.

	 *

	 * If the hash table bucket is full of kernel text entries, we'll

	 * lockup here but that shouldn't happen

	 */

	addis	r4,r7,next_slot@ha



1:	addis	r4,r7,next_slot@ha		/* get next evict slot */

	lwz	r6,next_slot@l(r4)

	addi	r6,r6,PTE_SIZE

	addi	r6,r6,PTE_SIZE			/* search for candidate */

	andi.	r6,r6,7*PTE_SIZE

	stw	r6,next_slot@l(r4)

	add	r4,r3,r6

	LDPTE	r0,PTE_SIZE/2(r4)		/* get PTE second word */

	clrrwi	r0,r0,12

	lis	r6,etext@h

	ori	r6,r6,etext@l			/* get etext */

	tophys(r6,r6)

	cmpl	cr0,r0,r6			/* compare and try again */

	blt	1b



#ifndef CONFIG_SMP

	/* Store PTE in PTEG */

arch/powerpc/mm/mem.c

+0 −3
Original line number Diff line number Diff line
@@ -58,9 +58,6 @@ int init_bootmem_done; 
int mem_init_done;

unsigned long memory_limit;



extern void hash_preload(struct mm_struct *mm, unsigned long ea,

			 unsigned long access, unsigned long trap);



int page_is_ram(unsigned long pfn)

{

	unsigned long paddr = (pfn << PAGE_SHIFT);

arch/powerpc/mm/mmu_decl.h

+4 −0
Original line number Diff line number Diff line
@@ -22,6 +22,10 @@ 
#include <asm/tlbflush.h>

#include <asm/mmu.h>



extern void hash_preload(struct mm_struct *mm, unsigned long ea,

			 unsigned long access, unsigned long trap);





#ifdef CONFIG_PPC32

extern void mapin_ram(void);

extern int map_page(unsigned long va, phys_addr_t pa, int flags);

arch/powerpc/mm/pgtable_32.c

+7 −4
Original line number Diff line number Diff line
@@ -282,16 +282,19 @@ int map_page(unsigned long va, phys_addr_t pa, int flags) 
void __init mapin_ram(void)

{

	unsigned long v, p, s, f;

	int ktext;



	s = mmu_mapin_ram();

	v = KERNELBASE + s;

	p = PPC_MEMSTART + s;

	for (; s < total_lowmem; s += PAGE_SIZE) {

		if ((char *) v >= _stext && (char *) v < etext)

			f = _PAGE_RAM_TEXT;

		else

			f = _PAGE_RAM;

		ktext = ((char *) v >= _stext && (char *) v < etext);

		f = ktext ?_PAGE_RAM_TEXT : _PAGE_RAM;

		map_page(v, p, f);

#ifdef CONFIG_PPC_STD_MMU_32

		if (ktext)

			hash_preload(&init_mm, v, 0, 0x300);

#endif

		v += PAGE_SIZE;

		p += PAGE_SIZE;

	}

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