From: Uros Bizjak <ubizjak@xxxxxxxxx>
[ Upstream commit f96fb2df3eb31ede1b34b0521560967310267750 ]
The detection of atomic update failure in reserve_eilvt_offset() is
not correct. The value returned by atomic_cmpxchg() should be compared
to the old value from the location to be updated.
If these two are the same, then atomic update succeeded and
"eilvt_offsets[offset]" location is updated to "new" in an atomic way.
Otherwise, the atomic update failed and it should be retried with the
value from "eilvt_offsets[offset]" - exactly what atomic_try_cmpxchg()
does in a correct and more optimal way.
Fixes: a68c439b1966c ("apic, x86: Check if EILVT APIC registers are available (AMD only)")
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230227160917.107820-1-ubizjak@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/x86/kernel/apic/apic.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index ed7d9cf71f68d..4df7d694369a5 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -412,10 +412,9 @@ static unsigned int reserve_eilvt_offset(int offset, unsigned int new)
if (vector && !eilvt_entry_is_changeable(vector, new))
/* may not change if vectors are different */
return rsvd;
- rsvd = atomic_cmpxchg(&eilvt_offsets[offset], rsvd, new);
- } while (rsvd != new);
+ } while (!atomic_try_cmpxchg(&eilvt_offsets[offset], &rsvd, new));
- rsvd &= ~APIC_EILVT_MASKED;
+ rsvd = new & ~APIC_EILVT_MASKED;
if (rsvd && rsvd != vector)
pr_info("LVT offset %d assigned for vector 0x%02x\n",
offset, rsvd);
--
2.39.2
