diff options
| -rw-r--r-- | arch/parisc/kernel/syscall.S | 25 |
1 files changed, 24 insertions, 1 deletions
diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S index b27f4aa..e767ab7 100644 --- a/arch/parisc/kernel/syscall.S +++ b/arch/parisc/kernel/syscall.S @@ -1,12 +1,35 @@ /* * Linux/PA-RISC Project (http://www.parisc-linux.org/) * - * System call entry code Copyright (c) Matthew Wilcox 1999 <willy@bofh.ai> + * System call entry code / Linux gateway page + * Copyright (c) Matthew Wilcox 1999 <willy@bofh.ai> * Licensed under the GNU GPL. * thanks to Philipp Rumpf, Mike Shaver and various others * sorry about the wall, puffin.. */ +/* +How does the Linux gateway page on PA-RISC work? +------------------------------------------------ +The Linux gateway page on PA-RISC is "special". +It actually has PAGE_GATEWAY bits set (this is linux terminology; in parisc +terminology it's Execute, promote to PL0) in the page map. So anything +executing on this page executes with kernel level privilege (there's more to it +than that: to have this happen, you also have to use a branch with a ,gate +completer to activate the privilege promotion). The upshot is that everything +that runs on the gateway page runs at kernel privilege but with the current +user process address space (although you have access to kernel space via %sr2). +For the 0x100 syscall entry, we redo the space registers to point to the kernel +address space (preserving the user address space in %sr3), move to wide mode if +required, save the user registers and branch into the kernel syscall entry +point. For all the other functions, we execute at kernel privilege but don't +flip address spaces. The basic upshot of this is that these code snippets are +executed atomically (because the kernel can't be pre-empted) and they may +perform architecturally forbidden (to PL3) operations (like setting control +registers). +*/ + + #include <asm/asm-offsets.h> #include <asm/unistd.h> #include <asm/errno.h> |