Since this isn't rt-only, and is part of the upstream kernel (but
apparently not nomiated for 5.4-stable backporting), I'd prefer
to merge this to all branches, versus just the intel-x86 preempt-rt.
I'll do that tomorrow, unless I hear objections.
Bruce
In message: [[linux-yocto][linux-yocto v5.4/standard/preempt-rt/intel-x86]
x86/alternatives: Acquire pte lock with interrupts enabled
on 07/04/2021 Jun Miao wrote:
> From: Sebastian Andrzej Siewior
>
> commit a6d996cbd38b42341ad3fce74506b9fdc280e395 upstream
>
> 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
> Signed-off-by: Thomas Gleixner
> Acked-by; Peter Zijlstra (Intel)
> Link: https://lore.kernel.org/r/20200813105026.bvugytmsso6mu...@linutronix.de
> Signed-off-by: Jun Miao
> ---
> arch/x86/kernel/alternative.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index c826cddae157..34a1b8562c31 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -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;
> }
>
> --
> 2.25.1
>
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