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KVM: PPC: Book3S HV: Workaround POWER9 DD1.0 bug causing IPB bit loss

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This adds a workaround for a bug in POWER9 DD1 chips where changing
the CPPR (Current Processor Priority Register) can cause bits in the
IPB (Interrupt Pending Buffer) to get lost.  Thankfully it only
happens when manually manipulating CPPR which is quite rare.  When it
does happen it can cause interrupts to be delayed or lost.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Benjamin Herrenschmidt 2017-08-18 12:10:52 +10:00 committed by Paul Mackerras
parent bd0fdb191c
commit 2c4fb78f78
1 changed files with 10 additions and 1 deletions
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11
arch/powerpc/kvm/book3s_xive_template.c
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@ -16,7 +16,16 @@ static void GLUE(X_PFX,ack_pending)(struct kvmppc_xive_vcpu *xc)
u8 cppr;
u16 ack;
/* XXX DD1 bug workaround: Check PIPR vs. CPPR first ! */
/*
* DD1 bug workaround: If PIPR is less favored than CPPR
* ignore the interrupt or we might incorrectly lose an IPB
* bit.
*/
if (cpu_has_feature(CPU_FTR_POWER9_DD1)) {
u8 pipr = __x_readb(__x_tima + TM_QW1_OS + TM_PIPR);
if (pipr >= xc->hw_cppr)
return;
}
/* Perform the acknowledge OS to register cycle. */
ack = be16_to_cpu(__x_readw(__x_tima + TM_SPC_ACK_OS_REG));