powerpc/xive: Prevent page fault issues in the machine crash handler

commit 1ca3dec2b2dff9d286ce6cd64108bda0e98f9710 upstream.

When the machine crash handler is invoked, all interrupts are masked
but interrupts which have not been started yet do not have an ESB page
mapped in the Linux address space. This crashes the 'crash kexec'
sequence on sPAPR guests.

To fix, force the mapping of the ESB page when an interrupt is being
mapped in the Linux IRQ number space. This is done by setting the
initial state of the interrupt to OFF which is not necessarily the
case on PowerNV.

Fixes: 243e2511 ("powerpc/xive: Native exploitation of the XIVE interrupt controller")
Cc: stable@vger.kernel.org # v4.12+
Signed-off-by: NCédric Le Goater <clg@kaod.org>
Reviewed-by: NGreg Kurz <groug@kaod.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191031063100.3864-1-clg@kaod.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/powerpc/sysdev/xive/common.c

@@ -968,6 +968,15 @@ static int xive_irq_alloc_data(unsigned int virq, irq_hw_number_t hw)
 	xd->target = XIVE_INVALID_TARGET;
 	irq_set_handler_data(virq, xd);
 
+	/*
+	 * Turn OFF by default the interrupt being mapped. A side
+	 * effect of this check is the mapping the ESB page of the
+	 * interrupt in the Linux address space. This prevents page
+	 * fault issues in the crash handler which masks all
+	 * interrupts.
+	 */
+	xive_esb_read(xd, XIVE_ESB_SET_PQ_01);
+
 	return 0;
 }