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Diffstat (limited to 'Documentation/core-api/entry.rst')
| -rw-r--r-- | Documentation/core-api/entry.rst | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/core-api/entry.rst b/Documentation/core-api/entry.rst index c6f8e22c88fe..e12f22ab33c7 100644 --- a/Documentation/core-api/entry.rst +++ b/Documentation/core-api/entry.rst @@ -105,6 +105,8 @@ has to do extra work between the various steps. In such cases it has to ensure that enter_from_user_mode() is called first on entry and exit_to_user_mode() is called last on exit. +Do not nest syscalls. Nested systcalls will cause RCU and/or context tracking +to print a warning. KVM --- @@ -121,6 +123,8 @@ Task work handling is done separately for guest at the boundary of the vcpu_run() loop via xfer_to_guest_mode_handle_work() which is a subset of the work handled on return to user space. +Do not nest KVM entry/exit transitions because doing so is nonsensical. + Interrupts and regular exceptions --------------------------------- @@ -180,6 +184,16 @@ before it handles soft interrupts, whose handlers must run in BH context rather than irq-disabled context. In addition, irqentry_exit() might schedule, which also requires that HARDIRQ_OFFSET has been removed from the preemption count. +Even though interrupt handlers are expected to run with local interrupts +disabled, interrupt nesting is common from an entry/exit perspective. For +example, softirq handling happens within an irqentry_{enter,exit}() block with +local interrupts enabled. Also, although uncommon, nothing prevents an +interrupt handler from re-enabling interrupts. + +Interrupt entry/exit code doesn't strictly need to handle reentrancy, since it +runs with local interrupts disabled. But NMIs can happen anytime, and a lot of +the entry code is shared between the two. + NMI and NMI-like exceptions --------------------------- @@ -259,3 +273,7 @@ and for e.g. a debug exception it can look like this: There is no combined irqentry_nmi_if_kernel() function available as the above cannot be handled in an exception-agnostic way. + +NMIs can happen in any context. For example, an NMI-like exception triggered +while handling an NMI. So NMI entry code has to be reentrant and state updates +need to handle nesting. |