diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2022-08-01 09:34:39 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-08-01 09:34:39 -0700 |
commit | 92598ae22f582547ebb060cf76f5869bc9780b80 (patch) | |
tree | 9328ae9102ae3e6c3b537764b48d936db8184c12 /Documentation | |
parent | 94e37e84891900f56a01f49ac173bcb15e42e461 (diff) | |
parent | 8f1d56f64f8d6b80dea2d1978d10071132a695c5 (diff) |
Merge tag 'x86_mm_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 mm updates from Borislav Petkov:
- Rename a PKRU macro to make more sense when reading the code
- Update pkeys documentation
- Avoid reading contended mm's TLB generation var if not absolutely
necessary along with fixing a case where arch_tlbbatch_flush()
doesn't adhere to the generation scheme and thus violates the
conditions for the above avoidance.
* tag 'x86_mm_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/mm/tlb: Ignore f->new_tlb_gen when zero
x86/pkeys: Clarify PKRU_AD_KEY macro
Documentation/protection-keys: Clean up documentation for User Space pkeys
x86/mm/tlb: Avoid reading mm_tlb_gen when possible
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/core-api/protection-keys.rst | 44 |
1 files changed, 21 insertions, 23 deletions
diff --git a/Documentation/core-api/protection-keys.rst b/Documentation/core-api/protection-keys.rst index ec575e72d0b2..bf28ac0401f3 100644 --- a/Documentation/core-api/protection-keys.rst +++ b/Documentation/core-api/protection-keys.rst @@ -4,31 +4,29 @@ Memory Protection Keys ====================== -Memory Protection Keys for Userspace (PKU aka PKEYs) is a feature -which is found on Intel's Skylake (and later) "Scalable Processor" -Server CPUs. It will be available in future non-server Intel parts -and future AMD processors. - -For anyone wishing to test or use this feature, it is available in -Amazon's EC2 C5 instances and is known to work there using an Ubuntu -17.04 image. - -Memory Protection Keys provides a mechanism for enforcing page-based -protections, but without requiring modification of the page tables -when an application changes protection domains. It works by -dedicating 4 previously ignored bits in each page table entry to a -"protection key", giving 16 possible keys. - -There is also a new user-accessible register (PKRU) with two separate -bits (Access Disable and Write Disable) for each key. Being a CPU -register, PKRU is inherently thread-local, potentially giving each +Memory Protection Keys provide a mechanism for enforcing page-based +protections, but without requiring modification of the page tables when an +application changes protection domains. + +Pkeys Userspace (PKU) is a feature which can be found on: + * Intel server CPUs, Skylake and later + * Intel client CPUs, Tiger Lake (11th Gen Core) and later + * Future AMD CPUs + +Pkeys work by dedicating 4 previously Reserved bits in each page table entry to +a "protection key", giving 16 possible keys. + +Protections for each key are defined with a per-CPU user-accessible register +(PKRU). Each of these is a 32-bit register storing two bits (Access Disable +and Write Disable) for each of 16 keys. + +Being a CPU register, PKRU is inherently thread-local, potentially giving each thread a different set of protections from every other thread. -There are two new instructions (RDPKRU/WRPKRU) for reading and writing -to the new register. The feature is only available in 64-bit mode, -even though there is theoretically space in the PAE PTEs. These -permissions are enforced on data access only and have no effect on -instruction fetches. +There are two instructions (RDPKRU/WRPKRU) for reading and writing to the +register. The feature is only available in 64-bit mode, even though there is +theoretically space in the PAE PTEs. These permissions are enforced on data +access only and have no effect on instruction fetches. Syscalls ======== |