linux-kernel - [PATCH v2] x86/alternatives: Let __text_poke() acquire the pte lock with enabled interrupts

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Date:   Thu, 13 Aug 2020 12:50:26 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH v2] x86/alternatives: Let __text_poke() acquire the pte lock
 with enabled interrupts

The pte lock is never acquired in-IRQ context so it does not require the
interrupts to be disabled.

RT complains here because the spinlock_t must not be acquired with
disabled interrupts.

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@...utronix.de>
---
v1…v2: Reword the patch description.

 arch/x86/kernel/alternative.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -875,8 +875,6 @@ static void *__text_poke(void *addr, con
 	 */
 	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.
@@ -893,6 +891,8 @@ static void *__text_poke(void *addr, con
 	 */
 	VM_BUG_ON(!ptep);
 
+	local_irq_save(flags);
+
 	pte = mk_pte(pages[0], pgprot);
 	set_pte_at(poking_mm, poking_addr, ptep, pte);
 
@@ -942,8 +942,8 @@ static void *__text_poke(void *addr, con
 	 */
 	BUG_ON(memcmp(addr, opcode, len));
 
-	pte_unmap_unlock(ptep, ptl);
 	local_irq_restore(flags);
+	pte_unmap_unlock(ptep, ptl);
 	return addr;
 }