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).

Cc: stable@vger.kernel.org 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.c... Signed-off-by: Joerg Roedel jroedel@suse.de --- Note: This patch is the back-port on top of the stable branch linux-5.4.y for the upstream commit e52d58d54a32 ("iommu/amd: Use cmpxchg_double() when updating 128-bit IRTE") since the original patch does not apply cleanly.

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

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig index 390568afee9f..fc0160e8ed33 100644 --- 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 diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c index fa91d856a43e..7b724f7b27a9 100644 --- a/drivers/iommu/amd_iommu.c +++ b/drivers/iommu/amd_iommu.c @@ -3873,6 +3873,7 @@ static int alloc_irq_index(u16 devid, int count, bool align, 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 index, struct irte_ga *irte,

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;

diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c index 135ae5222cf3..31d7e2d4f304 100644 --- 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 amd_iommu *iommu, struct ivhd_header *h) 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 amd_iommu *iommu, struct ivhd_header *h) 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