x86/ioperm: Move TSS bitmap update to exit to user work
There is no point to update the TSS bitmap for tasks which use I/O bitmaps
on every context switch. It's enough to update it right before exiting to
user space.
That reduces the context switch bitmap handling to invalidating the io
bitmap base offset in the TSS when the outgoing task has TIF_IO_BITMAP
set. The invaldiation is done on purpose when a task with an IO bitmap
switches out to prevent any possible leakage of an activated IO bitmap.
It also removes the requirement to update the tasks bitmap atomically in
ioperm().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 3f8e226..9747876 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -33,6 +33,7 @@
#include <asm/cpufeature.h>
#include <asm/fpu/api.h>
#include <asm/nospec-branch.h>
+#include <asm/io_bitmap.h>
#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>
@@ -196,6 +197,9 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
/* Reload ti->flags; we may have rescheduled above. */
cached_flags = READ_ONCE(ti->flags);
+ if (unlikely(cached_flags & _TIF_IO_BITMAP))
+ tss_update_io_bitmap();
+
fpregs_assert_state_consistent();
if (unlikely(cached_flags & _TIF_NEED_FPU_LOAD))
switch_fpu_return();