Re: [PATCH] pagemap: update documentation
On Thu, Jul 16, 2015 at 09:47:42PM +0300, Konstantin Khlebnikov wrote: > Notes about recent changes. > > Signed-off-by: Konstantin Khlebnikov > --- > Documentation/vm/pagemap.txt | 14 -- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt > index 3cfbbb333ea1..aab39aa7dd8f 100644 > --- a/Documentation/vm/pagemap.txt > +++ b/Documentation/vm/pagemap.txt > @@ -16,12 +16,17 @@ There are three components to pagemap: > * Bits 0-4 swap type if swapped > * Bits 5-54 swap offset if swapped > * Bit 55pte is soft-dirty (see Documentation/vm/soft-dirty.txt) > -* Bit 56page exlusively mapped > +* Bit 56page exclusively mapped (since 4.2) > * Bits 57-60 zero > -* Bit 61page is file-page or shared-anon > +* Bit 61page is file-page or shared-anon (since 3.5) > * Bit 62page swapped > * Bit 63page present > > + Since Linux 4.0 only users with the CAP_SYS_ADMIN capability can get PFNs: > + for unprivileged users from 4.0 till 4.2 open fails with -EPERM, starting I'm expecting that this patch will be merged before 4.2 is released, so if that's right, stating "till 4.2" might be incorrect. > + from from 4.2 PFN field is zeroed if user has no CAP_SYS_ADMIN capability. "from" duplicates ... Thanks, Naoya Horiguchi > + Reason: information about PFNs helps in exploiting Rowhammer > vulnerability. > + > If the page is not present but in swap, then the PFN contains an > encoding of the swap file number and the page's offset into the > swap. Unmapped pages return a null PFN. This allows determining > @@ -160,3 +165,8 @@ Other notes: > Reading from any of the files will return -EINVAL if you are not starting > the read on an 8-byte boundary (e.g., if you sought an odd number of bytes > into the file), or if the size of the read is not a multiple of 8 bytes. > + > +Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is > +always 12 at most architectures). Since Linux 3.11 their meaning changes > +after first clear of soft-dirty bits. Since Linux 4.2 they are used for > +flags unconditionally. > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] pagemap: update documentation
On Thu, Jul 16, 2015 at 09:47:42PM +0300, Konstantin Khlebnikov wrote: Notes about recent changes. Signed-off-by: Konstantin Khlebnikov khlebni...@yandex-team.ru --- Documentation/vm/pagemap.txt | 14 -- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt index 3cfbbb333ea1..aab39aa7dd8f 100644 --- a/Documentation/vm/pagemap.txt +++ b/Documentation/vm/pagemap.txt @@ -16,12 +16,17 @@ There are three components to pagemap: * Bits 0-4 swap type if swapped * Bits 5-54 swap offset if swapped * Bit 55pte is soft-dirty (see Documentation/vm/soft-dirty.txt) -* Bit 56page exlusively mapped +* Bit 56page exclusively mapped (since 4.2) * Bits 57-60 zero -* Bit 61page is file-page or shared-anon +* Bit 61page is file-page or shared-anon (since 3.5) * Bit 62page swapped * Bit 63page present + Since Linux 4.0 only users with the CAP_SYS_ADMIN capability can get PFNs: + for unprivileged users from 4.0 till 4.2 open fails with -EPERM, starting I'm expecting that this patch will be merged before 4.2 is released, so if that's right, stating till 4.2 might be incorrect. + from from 4.2 PFN field is zeroed if user has no CAP_SYS_ADMIN capability. from duplicates ... Thanks, Naoya Horiguchi + Reason: information about PFNs helps in exploiting Rowhammer vulnerability. + If the page is not present but in swap, then the PFN contains an encoding of the swap file number and the page's offset into the swap. Unmapped pages return a null PFN. This allows determining @@ -160,3 +165,8 @@ Other notes: Reading from any of the files will return -EINVAL if you are not starting the read on an 8-byte boundary (e.g., if you sought an odd number of bytes into the file), or if the size of the read is not a multiple of 8 bytes. + +Before Linux 3.11 pagemap bits 55-60 were used for page-shift (which is +always 12 at most architectures). Since Linux 3.11 their meaning changes +after first clear of soft-dirty bits. Since Linux 4.2 they are used for +flags unconditionally. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH] pagemap: update documentation
Notes about recent changes. Signed-off-by: Konstantin Khlebnikov --- Documentation/vm/pagemap.txt | 14 -- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt index 3cfbbb333ea1..aab39aa7dd8f 100644 --- a/Documentation/vm/pagemap.txt +++ b/Documentation/vm/pagemap.txt @@ -16,12 +16,17 @@ There are three components to pagemap: * Bits 0-4 swap type if swapped * Bits 5-54 swap offset if swapped * Bit 55pte is soft-dirty (see Documentation/vm/soft-dirty.txt) -* Bit 56page exlusively mapped +* Bit 56page exclusively mapped (since 4.2) * Bits 57-60 zero -* Bit 61page is file-page or shared-anon +* Bit 61page is file-page or shared-anon (since 3.5) * Bit 62page swapped * Bit 63page present + Since Linux 4.0 only users with the CAP_SYS_ADMIN capability can get PFNs: + for unprivileged users from 4.0 till 4.2 open fails with -EPERM, starting + from from 4.2 PFN field is zeroed if user has no CAP_SYS_ADMIN capability. + Reason: information about PFNs helps in exploiting Rowhammer vulnerability. + If the page is not present but in swap, then the PFN contains an encoding of the swap file number and the page's offset into the swap. Unmapped pages return a null PFN. This allows determining @@ -160,3 +165,8 @@ Other notes: Reading from any of the files will return -EINVAL if you are not starting the read on an 8-byte boundary (e.g., if you sought an odd number of bytes into the file), or if the size of the read is not a multiple of 8 bytes. + +Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is +always 12 at most architectures). Since Linux 3.11 their meaning changes +after first clear of soft-dirty bits. Since Linux 4.2 they are used for +flags unconditionally. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH] pagemap: update documentation
Notes about recent changes. Signed-off-by: Konstantin Khlebnikov khlebni...@yandex-team.ru --- Documentation/vm/pagemap.txt | 14 -- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt index 3cfbbb333ea1..aab39aa7dd8f 100644 --- a/Documentation/vm/pagemap.txt +++ b/Documentation/vm/pagemap.txt @@ -16,12 +16,17 @@ There are three components to pagemap: * Bits 0-4 swap type if swapped * Bits 5-54 swap offset if swapped * Bit 55pte is soft-dirty (see Documentation/vm/soft-dirty.txt) -* Bit 56page exlusively mapped +* Bit 56page exclusively mapped (since 4.2) * Bits 57-60 zero -* Bit 61page is file-page or shared-anon +* Bit 61page is file-page or shared-anon (since 3.5) * Bit 62page swapped * Bit 63page present + Since Linux 4.0 only users with the CAP_SYS_ADMIN capability can get PFNs: + for unprivileged users from 4.0 till 4.2 open fails with -EPERM, starting + from from 4.2 PFN field is zeroed if user has no CAP_SYS_ADMIN capability. + Reason: information about PFNs helps in exploiting Rowhammer vulnerability. + If the page is not present but in swap, then the PFN contains an encoding of the swap file number and the page's offset into the swap. Unmapped pages return a null PFN. This allows determining @@ -160,3 +165,8 @@ Other notes: Reading from any of the files will return -EINVAL if you are not starting the read on an 8-byte boundary (e.g., if you sought an odd number of bytes into the file), or if the size of the read is not a multiple of 8 bytes. + +Before Linux 3.11 pagemap bits 55-60 were used for page-shift (which is +always 12 at most architectures). Since Linux 3.11 their meaning changes +after first clear of soft-dirty bits. Since Linux 4.2 they are used for +flags unconditionally. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
