| Message ID | 1368006763-30774-9-git-send-email-steve.capper@linaro.org |
|---|---|
| State | New |
| Headers | show |
Hi Steve, On 05/08/2013 05:52 AM, Steve Capper wrote: > Under ARM64, PTEs can be broadly categorised as follows: > - Present and valid: Bit #0 is set. The PTE is valid and memory > access to the region may fault. > > - Present and invalid: Bit #0 is clear and bit #1 is set. > Represents present memory with PROT_NONE protection. The PTE > is an invalid entry, and the user fault handler will raise a > SIGSEGV. > > - Not present (file): Bits #0 and #1 are clear, bit #2 is set. > Memory represented has been paged out. The PTE is an invalid > entry, and the fault handler will try and re-populate the > memory where necessary. > > Huge PTEs are block descriptors that have bit #1 clear. If we wish > to represent PROT_NONE huge PTEs we then run into a problem as > there is no way to distinguish between regular and huge PTEs if we > set bit #1. > > As huge PTEs are always present, the meaning of bits #1 and #2 can > be swapped for invalid PTEs. This patch swaps the PTE_FILE and > PTE_PROT_NONE constants, allowing us to represent PROT_NONE huge > PTEs. [...] > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h [...] > @@ -306,8 +306,8 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD]; > > /* > * Encode and decode a file entry: > - * bits 0-1: present (must be zero) > - * bit 2: PTE_FILE > + * bits 0 & 2: present (must be zero) Consider using punctuation like "bits 0, 2" here to disambiguate from the binary and operation. [...] Christopher
On Wed, May 08, 2013 at 10:52:40AM +0100, Steve Capper wrote: > Under ARM64, PTEs can be broadly categorised as follows: > - Present and valid: Bit #0 is set. The PTE is valid and memory > access to the region may fault. > > - Present and invalid: Bit #0 is clear and bit #1 is set. > Represents present memory with PROT_NONE protection. The PTE > is an invalid entry, and the user fault handler will raise a > SIGSEGV. > > - Not present (file): Bits #0 and #1 are clear, bit #2 is set. > Memory represented has been paged out. The PTE is an invalid > entry, and the fault handler will try and re-populate the > memory where necessary. > > Huge PTEs are block descriptors that have bit #1 clear. If we wish > to represent PROT_NONE huge PTEs we then run into a problem as > there is no way to distinguish between regular and huge PTEs if we > set bit #1. > > As huge PTEs are always present, the meaning of bits #1 and #2 can > be swapped for invalid PTEs. This patch swaps the PTE_FILE and > PTE_PROT_NONE constants, allowing us to represent PROT_NONE huge > PTEs. > > Signed-off-by: Steve Capper <steve.capper@linaro.org> > --- > arch/arm64/include/asm/pgtable.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index b1a1b59..e245260 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -25,8 +25,8 @@ > * Software defined PTE bits definition. > */ > #define PTE_VALID (_AT(pteval_t, 1) << 0) > -#define PTE_PROT_NONE (_AT(pteval_t, 1) << 1) /* only when !PTE_VALID */ > -#define PTE_FILE (_AT(pteval_t, 1) << 2) /* only when !pte_present() */ > +#define PTE_FILE (_AT(pteval_t, 1) << 1) /* only when !pte_present() */ > +#define PTE_PROT_NONE (_AT(pteval_t, 1) << 2) /* only when !PTE_VALID */ > #define PTE_DIRTY (_AT(pteval_t, 1) << 55) > #define PTE_SPECIAL (_AT(pteval_t, 1) << 56) > > @@ -306,8 +306,8 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD]; > > /* > * Encode and decode a file entry: > - * bits 0-1: present (must be zero) > - * bit 2: PTE_FILE > + * bits 0 & 2: present (must be zero) > + * bit 1: PTE_FILE > * bits 3-63: file offset / PAGE_SIZE > */ > #define pte_file(pte) (pte_val(pte) & PTE_FILE) Can you update the comment describing swp entries too please? I *think* the __SWP_* defines can remain untouched, but the comment is now wrong. Will
On Wed, May 08, 2013 at 12:17:35PM -0400, Christopher Covington wrote: > Hi Steve, > > On 05/08/2013 05:52 AM, Steve Capper wrote: [...] > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > [...] > > > @@ -306,8 +306,8 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD]; > > > > /* > > * Encode and decode a file entry: > > - * bits 0-1: present (must be zero) > > - * bit 2: PTE_FILE > > + * bits 0 & 2: present (must be zero) > > Consider using punctuation like "bits 0, 2" here to disambiguate from the > binary and operation. > Hi Christopher, Thanks, I now have: bits 0, 2: present (must both be zero) Cheers,
On Wed, May 08, 2013 at 05:40:19PM +0100, Will Deacon wrote: > On Wed, May 08, 2013 at 10:52:40AM +0100, Steve Capper wrote: [...] > Can you update the comment describing swp entries too please? I *think* the > __SWP_* defines can remain untouched, but the comment is now wrong. > > Will Ta Will, I've now changed the other comment. The __SWP_* entries look ok to me. I'm going to run some swap tests though to see if anything crops up. Cheers,
On Wed, May 08, 2013 at 10:52:40AM +0100, Steve Capper wrote: > Under ARM64, PTEs can be broadly categorised as follows: > - Present and valid: Bit #0 is set. The PTE is valid and memory > access to the region may fault. > > - Present and invalid: Bit #0 is clear and bit #1 is set. > Represents present memory with PROT_NONE protection. The PTE > is an invalid entry, and the user fault handler will raise a > SIGSEGV. > > - Not present (file): Bits #0 and #1 are clear, bit #2 is set. > Memory represented has been paged out. The PTE is an invalid > entry, and the fault handler will try and re-populate the > memory where necessary. > > Huge PTEs are block descriptors that have bit #1 clear. If we wish > to represent PROT_NONE huge PTEs we then run into a problem as > there is no way to distinguish between regular and huge PTEs if we > set bit #1. > > As huge PTEs are always present, the meaning of bits #1 and #2 can > be swapped for invalid PTEs. This patch swaps the PTE_FILE and > PTE_PROT_NONE constants, allowing us to represent PROT_NONE huge > PTEs. I guess we'll never get a huge_(pte|pmd)_file() (but we can shift the file bits up anyway). > Signed-off-by: Steve Capper <steve.capper@linaro.org> Apart from the comments you already got: Acked-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index b1a1b59..e245260 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -25,8 +25,8 @@ * Software defined PTE bits definition. */ #define PTE_VALID (_AT(pteval_t, 1) << 0) -#define PTE_PROT_NONE (_AT(pteval_t, 1) << 1) /* only when !PTE_VALID */ -#define PTE_FILE (_AT(pteval_t, 1) << 2) /* only when !pte_present() */ +#define PTE_FILE (_AT(pteval_t, 1) << 1) /* only when !pte_present() */ +#define PTE_PROT_NONE (_AT(pteval_t, 1) << 2) /* only when !PTE_VALID */ #define PTE_DIRTY (_AT(pteval_t, 1) << 55) #define PTE_SPECIAL (_AT(pteval_t, 1) << 56) @@ -306,8 +306,8 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD]; /* * Encode and decode a file entry: - * bits 0-1: present (must be zero) - * bit 2: PTE_FILE + * bits 0 & 2: present (must be zero) + * bit 1: PTE_FILE * bits 3-63: file offset / PAGE_SIZE */ #define pte_file(pte) (pte_val(pte) & PTE_FILE)
Under ARM64, PTEs can be broadly categorised as follows: - Present and valid: Bit #0 is set. The PTE is valid and memory access to the region may fault. - Present and invalid: Bit #0 is clear and bit #1 is set. Represents present memory with PROT_NONE protection. The PTE is an invalid entry, and the user fault handler will raise a SIGSEGV. - Not present (file): Bits #0 and #1 are clear, bit #2 is set. Memory represented has been paged out. The PTE is an invalid entry, and the fault handler will try and re-populate the memory where necessary. Huge PTEs are block descriptors that have bit #1 clear. If we wish to represent PROT_NONE huge PTEs we then run into a problem as there is no way to distinguish between regular and huge PTEs if we set bit #1. As huge PTEs are always present, the meaning of bits #1 and #2 can be swapped for invalid PTEs. This patch swaps the PTE_FILE and PTE_PROT_NONE constants, allowing us to represent PROT_NONE huge PTEs. Signed-off-by: Steve Capper <steve.capper@linaro.org> --- arch/arm64/include/asm/pgtable.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)