x86/entry/64: Initialize the top of the IRQ stack before switching stacks

The OOPS unwinder wants the word at the top of the IRQ stack to
point back to the previous stack at all times when the IRQ stack
is in use.  There's currently a one-instruction window in ENTER_IRQ_STACK
during which this isn't the case.  Fix it by writing the old RSP to the
top of the IRQ stack before jumping.

This currently writes the pointer to the stack twice, which is a bit
ugly.  We could get rid of this by replacing irq_stack_ptr with
irq_stack_ptr_minus_eight (better name welcome).  OTOH, there may be
all kinds of odd microarchitectural considerations in play that
affect performance by a few cycles here.

Reported-by: Mike Galbraith <[email protected]>
Reported-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Andy Lutomirski <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/aae7e79e49914808440ad5310ace138ced2179ca.1499786555.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions