[PATCH 1/8] x86/irq: Ensure initial PIR loads are performed exactly once

[Sean Christopherson]

Ensure the PIR is read exactly once at the start of handle_pending_pir(),
to guarantee that checking for an outstanding posted interrupt in a given
chuck doesn't reload the chunk from the "real" PIR.  Functionally, a reload
is benign, but it would defeat the purpose of pre-loading into a copy.

Fixes: 1b03d82ba15e ("x86/irq: Install posted MSI notification handler")
Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kernel/irq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 385e3a5fc304..9e5263887ff6 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -412,7 +412,7 @@ static __always_inline bool handle_pending_pir(u64 *pir, struct pt_regs *regs)
 	bool handled = false;
 
 	for (i = 0; i < 4; i++)
-		pir_copy[i] = pir[i];
+		pir_copy[i] = READ_ONCE(pir[i]);
 
 	for (i = 0; i < 4; i++) {
 		if (!pir_copy[i])
-- 
2.49.0.rc1.451.g8f38331e32-goog