[PATCH 3/6] 8xx: get rid of _PAGE_HWWRITE dependency in MMU.
Joakim Tjernlund
joakim.tjernlund at transmode.se
Tue Oct 6 08:25:16 EST 2009
Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 05/10/2009 22:17:04:
>
> On Mon, 2009-10-05 at 14:16 +0200, Joakim Tjernlund wrote:
> > Update the TLB asm to make proper use of _PAGE_DIRY and _PAGE_ACCESSED.
> > Pros:
> > - I/D TLB Miss never needs to write to the linux pte.
> > - _PAGE_ACCESSED is only set on I/D TLB Error fixing accounting
> > - _PAGE_DIRTY is mapped to 0x100, the changed bit, and is set directly
> > when a page has been made dirty.
>
> Not sure here. You seem to still set those from asm. Is that necessary ?
Well, yes. head_32.S also sets ACCESSED and DIRTY from asm so why not me?
The basic method I use is:
TLB gets mapped with NoAccess, then the first access will trap
into TLB error, where ACCESSED will be set if permission to access
the page is OK (and RW too). On first store 8xx will trap
into DTLB error and permissions is OK, DIRTY will be set too.
Is this wrong?
Do I have to trap to C for first store?
>
> The approach I take on BookE is to simply not set these from asm, -and-
> (this is important) not set write permission if dirty is not set in
> the TLB miss and set no access permission at all when accessed is not
> set. This is important or we'll miss dirty updates which can
> be fatal.
not sure, but this seems similar to what I do. DIRTY will be set,
in asm, on first store.
ACCESSED will only be set iff (USER && VALID)
>
> The C code in handle_pte_fault() will fixup missing access and dirty
> if necessary and flush.
>
> Also look at the 440 code, I think you could simplify your
> implementation using similar techniques, such as andc of PTE against
> requested bits etc... and thus maybe save a couple of insns.
Great, but first I want to make sure I doing it right :)
So is there some golden rule I have to follow?
Jocke
>
> Cheers,
> Ben.
>
> > - Proper RO/RW mapping of user space.
> > - Free up 2 SW TLB bits in the linux pte(add back _PAGE_WRITETHRU ?)
> > Cons:
> > - 4 more instructions in I/D TLB Miss, but the since the linux pte is
> > not written anymore, it should still be a win.
> > ---
> > arch/powerpc/include/asm/pte-8xx.h | 9 +-
> > arch/powerpc/kernel/head_8xx.S | 163 ++++++++++++++++++++++++++----------
> > 2 files changed, 122 insertions(+), 50 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/pte-8xx.h b/arch/powerpc/include/asm/pte-8xx.h
> > index 8c6e312..af541a2 100644
> > --- a/arch/powerpc/include/asm/pte-8xx.h
> > +++ b/arch/powerpc/include/asm/pte-8xx.h
> > @@ -32,22 +32,21 @@
> > #define _PAGE_FILE 0x0002 /* when !present: nonlinear file mapping */
> > #define _PAGE_NO_CACHE 0x0002 /* I: cache inhibit */
> > #define _PAGE_SHARED 0x0004 /* No ASID (context) compare */
> > +#define _PAGE_DIRTY 0x0100 /* C: page changed */
> >
> > /* These five software bits must be masked out when the entry is loaded
> > * into the TLB.
> > */
> > #define _PAGE_EXEC 0x0008 /* software: i-cache coherency required */
> > #define _PAGE_GUARDED 0x0010 /* software: guarded access */
> > -#define _PAGE_DIRTY 0x0020 /* software: page changed */
> > -#define _PAGE_RW 0x0040 /* software: user write access allowed */
> > -#define _PAGE_ACCESSED 0x0080 /* software: page referenced */
> > +#define _PAGE_USER 0x0020 /* software: User space access */
> >
> > /* Setting any bits in the nibble with the follow two controls will
> > * require a TLB exception handler change. It is assumed unused bits
> > * are always zero.
> > */
> > -#define _PAGE_HWWRITE 0x0100 /* h/w write enable: never set in Linux PTE */
> > -#define _PAGE_USER 0x0800 /* One of the PP bits, the other is USER&~RW */
> > +#define _PAGE_RW 0x0400 /* lsb PP bits */
> > +#define _PAGE_ACCESSED 0x0800 /* msb PP bits */
> >
> > #define _PMD_PRESENT 0x0001
> > #define _PMD_BAD 0x0ff0
> > diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
> > index 118bb05..b1f72d9 100644
> > --- a/arch/powerpc/kernel/head_8xx.S
> > +++ b/arch/powerpc/kernel/head_8xx.S
> > @@ -333,21 +333,15 @@ InstructionTLBMiss:
> > mfspr r11, SPRN_MD_TWC /* ....and get the pte address */
> > lwz r10, 0(r11) /* Get the pte */
> >
> > -#ifdef CONFIG_SWAP
> > - /* do not set the _PAGE_ACCESSED bit of a non-present page */
> > - andi. r11, r10, _PAGE_PRESENT
> > - beq 4f
> > - ori r10, r10, _PAGE_ACCESSED
> > - mfspr r11, SPRN_MD_TWC /* get the pte address again */
> > - stw r10, 0(r11)
> > -4:
> > -#else
> > - ori r10, r10, _PAGE_ACCESSED
> > - stw r10, 0(r11)
> > -#endif
> > -
> > + andi. r11, r10, _PAGE_USER | _PAGE_ACCESSED
> > + cmpwi cr0, r11, _PAGE_USER | _PAGE_ACCESSED
> > + beq+ cr0, 5f /* branch if access allowed */
> > + rlwinm r10, r10, 0, 22, 19 /* r10 &= ~(_PAGE_ACCESSED | _PAGE_RW) */
> > + b 6f
> > +5: xori r10, r10, _PAGE_RW /* invert RW bit */
> > +6:
> > /* The Linux PTE won't go exactly into the MMU TLB.
> > - * Software indicator bits 21, 22 and 28 must be clear.
> > + * Software indicator bit 28 must be clear.
> > * Software indicator bits 24, 25, 26, and 27 must be
> > * set. All other Linux PTE bits control the behavior
> > * of the MMU.
> > @@ -409,21 +403,15 @@ DataStoreTLBMiss:
> > DO_8xx_CPU6(0x3b80, r3)
> > mtspr SPRN_MD_TWC, r11
> >
> > -#ifdef CONFIG_SWAP
> > - /* do not set the _PAGE_ACCESSED bit of a non-present page */
> > - andi. r11, r10, _PAGE_PRESENT
> > - beq 4f
> > - ori r10, r10, _PAGE_ACCESSED
> > -4:
> > - /* and update pte in table */
> > -#else
> > - ori r10, r10, _PAGE_ACCESSED
> > -#endif
> > - mfspr r11, SPRN_MD_TWC /* get the pte address again */
> > - stw r10, 0(r11)
> > -
> > + andi. r11, r10, _PAGE_USER | _PAGE_ACCESSED
> > + cmpwi cr0, r11, _PAGE_USER | _PAGE_ACCESSED
> > + beq+ cr0, 5f /* branch if access allowed */
> > + rlwinm r10, r10, 0, 22, 19 /* r10 &= ~(_PAGE_ACCESSED | _PAGE_RW) */
> > + b 6f
> > +5: xori r10, r10, _PAGE_RW /* invert RW bit */
> > +6:
> > /* The Linux PTE won't go exactly into the MMU TLB.
> > - * Software indicator bits 21, 22 and 28 must be clear.
> > + * Software indicator bit 28 must be clear.
> > * Software indicator bits 24, 25, 26, and 27 must be
> > * set. All other Linux PTE bits control the behavior
> > * of the MMU.
> > @@ -448,6 +436,91 @@ DataStoreTLBMiss:
> > */
> > . = 0x1300
> > InstructionTLBError:
> > +#ifdef CONFIG_8xx_CPU6
> > + stw r3, 8(r0)
> > +#endif
> > + DO_8xx_CPU6(0x3f80, r3)
> > + mtspr SPRN_M_TW, r10 /* Save a couple of working registers */
> > + mfcr r10
> > + stw r10, 0(r0)
> > + stw r11, 4(r0)
> > +
> > + mfspr r11, SPRN_SRR1
> > + andis. r11, r11, 0x5000 /* no translation, guarded */
> > + bne 2f
> > +
> > + mfspr r10, SPRN_SRR0 /* Get effective address of fault */
> > +#ifdef CONFIG_8xx_CPU15
> > + addi r11, r10, 0x1000
> > + tlbie r11
> > + addi r11, r10, -0x1000
> > + tlbie r11
> > +#endif
> > + DO_8xx_CPU6(0x3780, r3)
> > + mtspr SPRN_MD_EPN, r10 /* Have to use MD_EPN for walk, MI_EPN can't */
> > + mfspr r10, SPRN_M_TWB /* Get level 1 table entry address */
> > +
> > + /* If we are faulting a kernel address, we have to use the
> > + * kernel page tables.
> > + */
> > + andi. r11, r10, 0x0800 /* Address >= 0x80000000 */
> > + beq 3f
> > + lis r11, swapper_pg_dir at h
> > + ori r11, r11, swapper_pg_dir at l
> > + rlwimi r10, r11, 0, 2, 19
> > +3:
> > + lwz r11, 0(r10) /* Get the level 1 entry */
> > + rlwinm. r10, r11,0,0,19 /* Extract page descriptor page address */
> > + beq 2f /* If zero, don't try to find a pte */
> > +
> > + /* We have a pte table, so load the MI_TWC with the attributes
> > + * for this "segment."
> > + */
> > + ori r11,r11,1 /* Set valid bit */
> > + DO_8xx_CPU6(0x2b80, r3)
> > + mtspr SPRN_MI_TWC, r11 /* Set segment attributes */
> > + DO_8xx_CPU6(0x3b80, r3)
> > + mtspr SPRN_MD_TWC, r11 /* Load pte table base address */
> > +
> > + mfspr r11, SPRN_SRR1
> > + andi. r11, r11, 0x4000 /* MSR[PR] */
> > + mfspr r11, SPRN_MD_TWC /* ....and get the pte address */
> > + lwz r10, 0(r11) /* Get the pte */
> > + beq 5f /* Kernel access always OK */
> > + andi. r11,r10, _PAGE_USER
> > + beq 2f
> > +5: ori r10, r10, _PAGE_ACCESSED
> > + mfspr r21, SPRN_MD_TWC /* ....and get the pte address */
> > + stw r10, 0(r11)
> > + xori r10, r10, _PAGE_RW /* invert RW bit */
> > +
> > + /* The Linux PTE won't go exactly into the MMU TLB.
> > + * Software indicator bit 28 must be clear.
> > + * Software indicator bits 24, 25, 26, and 27 must be
> > + * set. All other Linux PTE bits control the behavior
> > + * of the MMU.
> > + */
> > + li r11, 0x00f0
> > + rlwimi r10, r11, 0, 24, 28 /* Set 24-27, clear 28 */
> > + DO_8xx_CPU6(0x2d80, r3)
> > + mtspr SPRN_MI_RPN, r10 /* Update TLB entry */
> > +
> > + mfspr r10, SPRN_M_TW /* Restore registers */
> > + lwz r11, 0(r0)
> > + mtcr r11
> > + lwz r11, 4(r0)
> > +#ifdef CONFIG_8xx_CPU6
> > + lwz r3, 8(r0)
> > +#endif
> > + rfi
> > +
> > +2: mfspr r10, SPRN_M_TW /* Restore registers */
> > + lwz r11, 0(r0)
> > + mtcr r11
> > + lwz r11, 4(r0)
> > +#ifdef CONFIG_8xx_CPU6
> > + lwz r3, 8(r0)
> > +#endif
> > b InstructionAccess
> >
> > /* This is the data TLB error on the MPC8xx. This could be due to
> > @@ -472,8 +545,8 @@ DataTLBError:
> > /* First, make sure this was a store operation.
> > */
> > mfspr r10, SPRN_DSISR
> > - andis. r11, r10, 0x4800 /* no translation, no permission. */
> > - bne 2f /* branch if either is set */
> > + andis. r11, r10, 0x4000 /* no translation */
> > + bne 2f /* branch if set */
> >
> > /* The EA of a data TLB miss is automatically stored in the MD_EPN
> > * register. The EA of a data TLB error is automatically stored in
> > @@ -522,26 +595,26 @@ DataTLBError:
> > mfspr r11, SPRN_MD_TWC /* ....and get the pte address */
> > lwz r10, 0(r11) /* Get the pte */
> >
> > - andi. r11, r10, _PAGE_RW /* Is it writeable? */
> > - beq 2f /* Bail out if not */
> > + mfspr r11, SPRN_SRR1
> > + andi. r11, r11, 0x4000 /* MSR[PR] */
> > + beq 5f /* Kernel access always OK */
> > + andi. r11,r10, _PAGE_USER
> > + beq 2f
> > +5: mfspr r11, SPRN_DSISR
> > + andis. r11, r11, 0x0200 /* store */
> > + beq 6f
> > + andi. r11, r10, _PAGE_RW /* writeable? */
> > + beq 2f /* branch if not */
> > + ori r10, r10, _PAGE_DIRTY | _PAGE_HWWRITE
> > +6: ori r10, r10, _PAGE_ACCESSED
> >
> > - /* Update 'changed', among others.
> > - */
> > -#ifdef CONFIG_SWAP
> > - ori r10, r10, _PAGE_DIRTY|_PAGE_HWWRITE
> > - /* do not set the _PAGE_ACCESSED bit of a non-present page */
> > - andi. r11, r10, _PAGE_PRESENT
> > - beq 4f
> > - ori r10, r10, _PAGE_ACCESSED
> > -4:
> > -#else
> > - ori r10, r10, _PAGE_DIRTY|_PAGE_ACCESSED|_PAGE_HWWRITE
> > -#endif
> > mfspr r11, SPRN_MD_TWC /* Get pte address again */
> > stw r10, 0(r11) /* and update pte in table */
> >
> > + xori r10, r10, _PAGE_RW /* Invert RW bit */
> > +
> > /* The Linux PTE won't go exactly into the MMU TLB.
> > - * Software indicator bits 21, 22 and 28 must be clear.
> > + * Software indicator bit 28 must be clear.
> > * Software indicator bits 24, 25, 26, and 27 must be
> > * set. All other Linux PTE bits control the behavior
> > * of the MMU.
>
>
>
>
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