[PATCH 5.4 43/43] iommu/amd: Use cmpxchg_double() when updating 128-bit IRTE

Greg Kroah-Hartman
2020-09-25T12:53:35Z

From: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>

commit e52d58d54a321d4fe9d0ecdabe4f8774449f0d6e upstream.

When using 128-bit interrupt-remapping table entry (IRTE) (a.k.a GA mode),
current driver disables interrupt remapping when it updates the IRTE
so that the upper and lower 64-bit values can be updated safely.

However, this creates a small window, where the interrupt could
arrive and result in IO_PAGE_FAULT (for interrupt) as shown below.

IOMMU Driver Device IRQ
============ ===========
irte.RemapEn=0
...
change IRTE IRQ from device ==> IO_PAGE_FAULT !!
...
irte.RemapEn=1

This scenario has been observed when changing irq affinity on a system
running I/O-intensive workload, in which the destination APIC ID
in the IRTE is updated.

Instead, use cmpxchg_double() to update the 128-bit IRTE at once without
disabling the interrupt remapping. However, this means several features,
which require GA (128-bit IRTE) support will also be affected if cmpxchg16b
is not supported (which is unprecedented for AMD processors w/ IOMMU).

Fixes: 880ac60e2538 ("iommu/amd: Introduce interrupt remapping ops structure")
Reported-by: Sean Osborne <sean.m.osborne@oracle.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Tested-by: Erik Rockstrom <erik.rockstrom@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Link: https://lore.kernel.org/r/20200903093822.52012-3-suravee.suthikulpanit@amd.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/iommu/Kconfig | 2 +-
drivers/iommu/amd_iommu.c | 17 +++++++++++++----
drivers/iommu/amd_iommu_init.c | 21 +++++++++++++++++++--
3 files changed, 33 insertions(+), 7 deletions(-)

--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -138,7 +138,7 @@ config AMD_IOMMU
select PCI_PASID
select IOMMU_API
select IOMMU_IOVA
- depends on X86_64 && PCI && ACPI
+ depends on X86_64 && PCI && ACPI && HAVE_CMPXCHG_DOUBLE
---help---
With this option you can enable support for AMD IOMMU hardware in
your system. An IOMMU is a hardware component which provides
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -3873,6 +3873,7 @@ out:
static int modify_irte_ga(u16 devid, int index, struct irte_ga *irte,
struct amd_ir_data *data)
{
+ bool ret;
struct irq_remap_table *table;
struct amd_iommu *iommu;
unsigned long flags;
@@ -3890,10 +3891,18 @@ static int modify_irte_ga(u16 devid, int

entry = (struct irte_ga *)table->table;
entry = &entry[index];
- entry->lo.fields_remap.valid = 0;
- entry->hi.val = irte->hi.val;
- entry->lo.val = irte->lo.val;
- entry->lo.fields_remap.valid = 1;
+
+ ret = cmpxchg_double(&entry->lo.val, &entry->hi.val,
+ entry->lo.val, entry->hi.val,
+ irte->lo.val, irte->hi.val);
+ /*
+ * We use cmpxchg16 to atomically update the 128-bit IRTE,
+ * and it cannot be updated by the hardware or other processors
+ * behind us, so the return value of cmpxchg16 should be the
+ * same as the old value.
+ */
+ WARN_ON(!ret);
+
if (data)
data->ref = entry;

--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -1522,7 +1522,14 @@ static int __init init_iommu_one(struct
iommu->mmio_phys_end = MMIO_REG_END_OFFSET;
else
iommu->mmio_phys_end = MMIO_CNTR_CONF_OFFSET;
- if (((h->efr_attr & (0x1 << IOMMU_FEAT_GASUP_SHIFT)) == 0))
+
+ /*
+ * Note: GA (128-bit IRTE) mode requires cmpxchg16b supports.
+ * GAM also requires GA mode. Therefore, we need to
+ * check cmpxchg16b support before enabling it.
+ */
+ if (!boot_cpu_has(X86_FEATURE_CX16) ||
+ ((h->efr_attr & (0x1 << IOMMU_FEAT_GASUP_SHIFT)) == 0))
amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY;
break;
case 0x11:
@@ -1531,8 +1538,18 @@ static int __init init_iommu_one(struct
iommu->mmio_phys_end = MMIO_REG_END_OFFSET;
else
iommu->mmio_phys_end = MMIO_CNTR_CONF_OFFSET;
- if (((h->efr_reg & (0x1 << IOMMU_EFR_GASUP_SHIFT)) == 0))
+
+ /*
+ * Note: GA (128-bit IRTE) mode requires cmpxchg16b supports.
+ * XT, GAM also requires GA mode. Therefore, we need to
+ * check cmpxchg16b support before enabling them.
+ */
+ if (!boot_cpu_has(X86_FEATURE_CX16) ||
+ ((h->efr_reg & (0x1 << IOMMU_EFR_GASUP_SHIFT)) == 0)) {
amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY;
+ break;
+ }
+
/*
* Note: Since iommu_update_intcapxt() leverages
* the IOMMU MMIO access to MSI capability block registers