diff options
Diffstat (limited to 'Documentation/x86')
| -rw-r--r-- | Documentation/x86/entry_64.txt | 18 | ||||
| -rw-r--r-- | Documentation/x86/x86_64/kernel-stacks | 8 |
2 files changed, 17 insertions, 9 deletions
diff --git a/Documentation/x86/entry_64.txt b/Documentation/x86/entry_64.txt index 4a1c5c2dc5a9..9132b86176a3 100644 --- a/Documentation/x86/entry_64.txt +++ b/Documentation/x86/entry_64.txt @@ -78,9 +78,6 @@ The expensive (paranoid) way is to read back the MSR_GS_BASE value xorl %ebx,%ebx 1: ret -and the whole paranoid non-paranoid macro complexity is about whether -to suffer that RDMSR cost. - If we are at an interrupt or user-trap/gate-alike boundary then we can use the faster check: the stack will be a reliable indicator of whether SWAPGS was already done: if we see that we are a secondary @@ -93,6 +90,15 @@ which might have triggered right after a normal entry wrote CS to the stack but before we executed SWAPGS, then the only safe way to check for GS is the slower method: the RDMSR. -So we try only to mark those entry methods 'paranoid' that absolutely -need the more expensive check for the GS base - and we generate all -'normal' entry points with the regular (faster) entry macros. +Therefore, super-atomic entries (except NMI, which is handled separately) +must use idtentry with paranoid=1 to handle gsbase correctly. This +triggers three main behavior changes: + + - Interrupt entry will use the slower gsbase check. + - Interrupt entry from user mode will switch off the IST stack. + - Interrupt exit to kernel mode will not attempt to reschedule. + +We try to only use IST entries and the paranoid entry code for vectors +that absolutely need the more expensive check for the GS base - and we +generate all 'normal' entry points with the regular (faster) paranoid=0 +variant. diff --git a/Documentation/x86/x86_64/kernel-stacks b/Documentation/x86/x86_64/kernel-stacks index a01eec5d1d0b..e3c8a49d1a2f 100644 --- a/Documentation/x86/x86_64/kernel-stacks +++ b/Documentation/x86/x86_64/kernel-stacks @@ -40,9 +40,11 @@ An IST is selected by a non-zero value in the IST field of an interrupt-gate descriptor. When an interrupt occurs and the hardware loads such a descriptor, the hardware automatically sets the new stack pointer based on the IST value, then invokes the interrupt handler. If -software wants to allow nested IST interrupts then the handler must -adjust the IST values on entry to and exit from the interrupt handler. -(This is occasionally done, e.g. for debug exceptions.) +the interrupt came from user mode, then the interrupt handler prologue +will switch back to the per-thread stack. If software wants to allow +nested IST interrupts then the handler must adjust the IST values on +entry to and exit from the interrupt handler. (This is occasionally +done, e.g. for debug exceptions.) Events with different IST codes (i.e. with different stacks) can be nested. For example, a debug interrupt can safely be interrupted by an |