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x86/alternatives: Acquire pte lock with interrupts enabled 

pte lock is never acquired in-IRQ context so it does not require interrupts
to be disabled. The lock is a regular spinlock which cannot be acquired
with interrupts disabled on RT.

RT complains about pte_lock() in __text_poke() because it's invoked after
disabling interrupts.

__text_poke() has to disable interrupts as use_temporary_mm() expects
interrupts to be off because it invokes switch_mm_irqs_off() and uses
per-CPU (current active mm) data.

Move the PTE lock handling outside the interrupt disabled region.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by; Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200813105026.bvugytmsso6muljw@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2020-08-13 12:50:26 +02:00 committed by Thomas Gleixner
parent f29dfa53cc
commit a6d996cbd3
1 changed files with 3 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/x86/kernel/alternative.c
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@ -874,8 +874,6 @@ static void *__text_poke(void *addr, const void *opcode, size_t len)
*/
BUG_ON(!pages[0] || (cross_page_boundary && !pages[1]));
local_irq_save(flags);
/*
* Map the page without the global bit, as TLB flushing is done with
* flush_tlb_mm_range(), which is intended for non-global PTEs.
@ -892,6 +890,8 @@ static void *__text_poke(void *addr, const void *opcode, size_t len)
*/
VM_BUG_ON(!ptep);
local_irq_save(flags);
pte = mk_pte(pages[0], pgprot);
set_pte_at(poking_mm, poking_addr, ptep, pte);
@ -941,8 +941,8 @@ static void *__text_poke(void *addr, const void *opcode, size_t len)
*/
BUG_ON(memcmp(addr, opcode, len));
pte_unmap_unlock(ptep, ptl);
local_irq_restore(flags);
pte_unmap_unlock(ptep, ptl);
return addr;
}