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x86/apic: Fix atomic update of offset in reserve_eilvt_offset()

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[ 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@gmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230227160917.107820-1-ubizjak@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Uros Bizjak 2023-02-27 17:09:17 +01:00 committed by Greg Kroah-Hartman
parent 0b94849431
commit b940919d8a
1 changed files with 2 additions and 3 deletions
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5
arch/x86/kernel/apic/apic.c
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@ -403,10 +403,9 @@ 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);