iommu: Actually clear IO-APIC pins on boot and shutdown when used with an IOMMU

When booted with iommu=on, io_apic_read/write functions call into the
interrupt remapping code to update the IRTEs.  Unfortunately, on boot
and shutdown, we really want clear_IO_APIC() to sanitize the actual
IOAPIC RTE, and not just the bits that are active when interrupt
remapping is enabled.  This is particularly a problem on older
versions of Xen which used the IOAPIC RTE as the canonical source for
the IRTE index.  In that case, clear_IO_APIC() actually causes
whatever happens to be stored in the RTEs to be used as an IRTE index,
which can come back and bite us in ioapic_guest_write() if we attempt
to remove an interrupt that didn't actually exist.  Current upstream
appears less susceptible to errors since the IRTE index is stored in
an array, but it's still a good idea to sanitize the IOAPIC state.

Signed-off-by: Alex Williamson <alex.williamson@hp.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/xen/include/asm-x86/io_apic.h b/xen/include/asm-x86/io_apic.h
index e47ee0c168..d546380435 100644
--- a/xen/include/asm-x86/io_apic.h
+++ b/xen/include/asm-x86/io_apic.h
@@ -131,20 +131,30 @@ extern struct mpc_config_ioapic mp_ioapics[MAX_IO_APICS];
 /* Only need to remap ioapic RTE (reg: 10~3Fh) */
 #define ioapic_reg_remapped(reg) (iommu_enabled && ((reg) >= 0x10))
 
+static inline unsigned int __io_apic_read(unsigned int apic, unsigned int reg)
+{
+	*IO_APIC_BASE(apic) = reg;
+	return *(IO_APIC_BASE(apic)+4);
+}
+
 static inline unsigned int io_apic_read(unsigned int apic, unsigned int reg)
 {
 	if (ioapic_reg_remapped(reg))
 		return iommu_read_apic_from_ire(apic, reg);
+	return __io_apic_read(apic, reg);
+}
+
+static inline void __io_apic_write(unsigned int apic, unsigned int reg, unsigned int value)
+{
 	*IO_APIC_BASE(apic) = reg;
-	return *(IO_APIC_BASE(apic)+4);
+	*(IO_APIC_BASE(apic)+4) = value;
 }
 
 static inline void io_apic_write(unsigned int apic, unsigned int reg, unsigned int value)
 {
 	if (ioapic_reg_remapped(reg))
 		return iommu_update_ire_from_apic(apic, reg, value);
-	*IO_APIC_BASE(apic) = reg;
-	*(IO_APIC_BASE(apic)+4) = value;
+	__io_apic_write(apic, reg, value);
 }
 
 static inline void io_apic_eoi(unsigned int apic, unsigned int vector)