This is a note to let you know that I've just added the patch titled iommu/amd: Use cmpxchg_double() when updating 128-bit IRTE to the 5.8-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: iommu-amd-use-cmpxchg_double-when-updating-128-bit-i.patch and it can be found in the queue-5.8 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 31640157d429339f8fffc14a645cb2c9739e0f17 Author: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx> Date: Thu Sep 3 09:38:22 2020 +0000 iommu/amd: Use cmpxchg_double() when updating 128-bit IRTE [ Upstream commit e52d58d54a321d4fe9d0ecdabe4f8774449f0d6e ] 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@xxxxxxxxxx> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx> Tested-by: Erik Rockstrom <erik.rockstrom@xxxxxxxxxx> Reviewed-by: Joao Martins <joao.m.martins@xxxxxxxxxx> Link: https://lore.kernel.org/r/20200903093822.52012-3-suravee.suthikulpanit@xxxxxxx Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig index b0f308cb7f7c2..201b2718f0755 100644 --- a/drivers/iommu/Kconfig +++ b/drivers/iommu/Kconfig @@ -143,7 +143,7 @@ config AMD_IOMMU select IOMMU_API select IOMMU_IOVA select IOMMU_DMA - 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/init.c b/drivers/iommu/amd/init.c index 6ebd4825e3206..bf45f8e2c7edd 100644 --- a/drivers/iommu/amd/init.c +++ b/drivers/iommu/amd/init.c @@ -1518,7 +1518,14 @@ 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: @@ -1527,8 +1534,18 @@ 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 diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c index d7b037891fb7e..200ee948f6ec1 100644 --- a/drivers/iommu/amd/iommu.c +++ b/drivers/iommu/amd/iommu.c @@ -3283,6 +3283,7 @@ 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; @@ -3300,10 +3301,18 @@ 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;