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Commit bb9b52bd authored by Benjamin Herrenschmidt's avatar Benjamin Herrenschmidt Committed by Paul Mackerras
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KVM: PPC: Book3S HV: Add missing barriers to XIVE code and document them 



This adds missing memory barriers to order updates/tests of
the virtual CPPR and MFRR, thus fixing a lost IPI problem.

While at it also document all barriers in this file.

This fixes a bug causing guest IPIs to occasionally get lost.  The
symptom then is hangs or stalls in the guest.

Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
Tested-by: default avatarGuilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
parent 2c4fb78f

arch/powerpc/kvm/book3s_xive_template.c

+55 −2
Original line number Diff line number Diff line
@@ -16,6 +16,12 @@ static void GLUE(X_PFX,ack_pending)(struct kvmppc_xive_vcpu *xc) 
	u8 cppr;

	u16 ack;



	/*

	 * Ensure any previous store to CPPR is ordered vs.

	 * the subsequent loads from PIPR or ACK.

	 */

	eieio();



	/*

	 * DD1 bug workaround: If PIPR is less favored than CPPR

	 * ignore the interrupt or we might incorrectly lose an IPB
@@ -244,6 +250,11 @@ static u32 GLUE(X_PFX,scan_interrupts)(struct kvmppc_xive_vcpu *xc, 
	/*

	 * If we found an interrupt, adjust what the guest CPPR should

	 * be as if we had just fetched that interrupt from HW.

	 *

	 * Note: This can only make xc->cppr smaller as the previous

	 * loop will only exit with hirq != 0 if prio is lower than

	 * the current xc->cppr. Thus we don't need to re-check xc->mfrr

	 * for pending IPIs.

	 */

	if (hirq)

		xc->cppr = prio;
@@ -389,6 +400,12 @@ X_STATIC int GLUE(X_PFX,h_cppr)(struct kvm_vcpu *vcpu, unsigned long cppr) 
	old_cppr = xc->cppr;

	xc->cppr = cppr;



	/*

	 * Order the above update of xc->cppr with the subsequent

	 * read of xc->mfrr inside push_pending_to_hw()

	 */

	smp_mb();



	/*

	 * We are masking less, we need to look for pending things

	 * to deliver and set VP pending bits accordingly to trigger
@@ -429,21 +446,37 @@ X_STATIC int GLUE(X_PFX,h_eoi)(struct kvm_vcpu *vcpu, unsigned long xirr) 
	 * used to signal MFRR changes is EOId when fetched from

	 * the queue.

	 */

	if (irq == XICS_IPI || irq == 0)

	if (irq == XICS_IPI || irq == 0) {

		/*

		 * This barrier orders the setting of xc->cppr vs.

		 * subsquent test of xc->mfrr done inside

		 * scan_interrupts and push_pending_to_hw

		 */

		smp_mb();

		goto bail;

	}



	/* Find interrupt source */

	sb = kvmppc_xive_find_source(xive, irq, &src);

	if (!sb) {

		pr_devel(" source not found !\n");

		rc = H_PARAMETER;

		/* Same as above */

		smp_mb();

		goto bail;

	}

	state = &sb->irq_state[src];

	kvmppc_xive_select_irq(state, &hw_num, &xd);



	state->in_eoi = true;

	mb();



	/*

	 * This barrier orders both setting of in_eoi above vs,

	 * subsequent test of guest_priority, and the setting

	 * of xc->cppr vs. subsquent test of xc->mfrr done inside

	 * scan_interrupts and push_pending_to_hw

	 */

	smp_mb();



again:

	if (state->guest_priority == MASKED) {
@@ -470,6 +503,14 @@ X_STATIC int GLUE(X_PFX,h_eoi)(struct kvm_vcpu *vcpu, unsigned long xirr) 


	}



	/*

	 * This barrier orders the above guest_priority check

	 * and spin_lock/unlock with clearing in_eoi below.

	 *

	 * It also has to be a full mb() as it must ensure

	 * the MMIOs done in source_eoi() are completed before

	 * state->in_eoi is visible.

	 */

	mb();

	state->in_eoi = false;

bail:
@@ -504,6 +545,18 @@ X_STATIC int GLUE(X_PFX,h_ipi)(struct kvm_vcpu *vcpu, unsigned long server, 
	/* Locklessly write over MFRR */

	xc->mfrr = mfrr;



	/*

	 * The load of xc->cppr below and the subsequent MMIO store

	 * to the IPI must happen after the above mfrr update is

	 * globally visible so that:

	 *

	 * - Synchronize with another CPU doing an H_EOI or a H_CPPR

	 *   updating xc->cppr then reading xc->mfrr.

	 *

	 * - The target of the IPI sees the xc->mfrr update

	 */

	mb();



	/* Shoot the IPI if most favored than target cppr */

	if (mfrr < xc->cppr)

		__x_writeq(0, __x_trig_page(&xc->vp_ipi_data));