diff options
Diffstat (limited to 'Documentation/x86')
| -rw-r--r-- | Documentation/x86/intel_mpx.txt | 4 | ||||
| -rw-r--r-- | Documentation/x86/pat.txt | 32 | ||||
| -rw-r--r-- | Documentation/x86/protection-keys.txt | 27 | ||||
| -rw-r--r-- | Documentation/x86/x86_64/mm.txt | 6 |
4 files changed, 64 insertions, 5 deletions
diff --git a/Documentation/x86/intel_mpx.txt b/Documentation/x86/intel_mpx.txt index 818518a3ff01..1a5a12184a35 100644 --- a/Documentation/x86/intel_mpx.txt +++ b/Documentation/x86/intel_mpx.txt @@ -136,7 +136,7 @@ A: MPX-enabled application will possibly create a lot of bounds tables in If we were to preallocate them for the 128TB of user virtual address space, we would need to reserve 512TB+2GB, which is larger than the entire virtual address space today. This means they can not be reserved - ahead of time. Also, a single process's pre-popualated bounds directory + ahead of time. Also, a single process's pre-populated bounds directory consumes 2GB of virtual *AND* physical memory. IOW, it's completely infeasible to prepopulate bounds directories. @@ -151,7 +151,7 @@ A: This would work if we could hook the site of each and every memory these calls. Q: Could a bounds fault be handed to userspace and the tables allocated - there in a signal handler intead of in the kernel? + there in a signal handler instead of in the kernel? A: mmap() is not on the list of safe async handler functions and even if mmap() would work it still requires locking or nasty tricks to keep track of the allocation state there. diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt index 54944c71b819..2a4ee6302122 100644 --- a/Documentation/x86/pat.txt +++ b/Documentation/x86/pat.txt @@ -196,3 +196,35 @@ Another, more verbose way of getting PAT related debug messages is with "debugpat" boot parameter. With this parameter, various debug messages are printed to dmesg log. +PAT Initialization +------------------ + +The following table describes how PAT is initialized under various +configurations. The PAT MSR must be updated by Linux in order to support WC +and WT attributes. Otherwise, the PAT MSR has the value programmed in it +by the firmware. Note, Xen enables WC attribute in the PAT MSR for guests. + + MTRR PAT Call Sequence PAT State PAT MSR + ========================================================= + E E MTRR -> PAT init Enabled OS + E D MTRR -> PAT init Disabled - + D E MTRR -> PAT disable Disabled BIOS + D D MTRR -> PAT disable Disabled - + - np/E PAT -> PAT disable Disabled BIOS + - np/D PAT -> PAT disable Disabled - + E !P/E MTRR -> PAT init Disabled BIOS + D !P/E MTRR -> PAT disable Disabled BIOS + !M !P/E MTRR stub -> PAT disable Disabled BIOS + + Legend + ------------------------------------------------ + E Feature enabled in CPU + D Feature disabled/unsupported in CPU + np "nopat" boot option specified + !P CONFIG_X86_PAT option unset + !M CONFIG_MTRR option unset + Enabled PAT state set to enabled + Disabled PAT state set to disabled + OS PAT initializes PAT MSR with OS setting + BIOS PAT keeps PAT MSR with BIOS setting + diff --git a/Documentation/x86/protection-keys.txt b/Documentation/x86/protection-keys.txt new file mode 100644 index 000000000000..c281ded1ba16 --- /dev/null +++ b/Documentation/x86/protection-keys.txt @@ -0,0 +1,27 @@ +Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature +which will be found on future Intel CPUs. + +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 +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. + +=========================== Config Option =========================== + +This config option adds approximately 1.5kb of text. and 50 bytes of +data to the executable. A workload which does large O_DIRECT reads +of holes in XFS files was run to exercise get_user_pages_fast(). No +performance delta was observed with the config option +enabled or disabled. diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt index c518dce7da4d..5aa738346062 100644 --- a/Documentation/x86/x86_64/mm.txt +++ b/Documentation/x86/x86_64/mm.txt @@ -19,7 +19,7 @@ ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks ffffffef00000000 - ffffffff00000000 (=64 GB) EFI region mapping space ... unused hole ... ffffffff80000000 - ffffffffa0000000 (=512 MB) kernel text mapping, from phys 0 -ffffffffa0000000 - ffffffffff5fffff (=1525 MB) module mapping space +ffffffffa0000000 - ffffffffff5fffff (=1526 MB) module mapping space ffffffffff600000 - ffffffffffdfffff (=8 MB) vsyscalls ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole @@ -31,8 +31,8 @@ vmalloc space is lazily synchronized into the different PML4 pages of the processes using the page fault handler, with init_level4_pgt as reference. -Current X86-64 implementations only support 40 bits of address space, -but we support up to 46 bits. This expands into MBZ space in the page tables. +Current X86-64 implementations support up to 46 bits of address space (64 TB), +which is our current limit. This expands into MBZ space in the page tables. We map EFI runtime services in the 'efi_pgd' PGD in a 64Gb large virtual memory window (this size is arbitrary, it can be raised later if needed). |