[v2,3/5] iommu/amd: Introduce Disable IRTE Caching Support
Commit Message
An Interrupt Remapping Table (IRT) stores interrupt remapping configuration
for each device. In a normal operation, the AMD IOMMU caches the table
to optimize subsequent data accesses. This requires the IOMMU driver to
invalidate IRT whenever it updates the table. The invalidation process
includes issuing an INVALIDATE_INTERRUPT_TABLE command following by
a COMPLETION_WAIT command.
However, there are cases in which the IRT is updated at a high rate.
For example, for IOMMU AVIC, the IRTE[IsRun] bit is updated on every
vcpu scheduling (i.e. amd_iommu_update_ga()). On system with large
amount of vcpus and VFIO PCI pass-through devices, the invalidation
process could potentially become a performance bottleneck.
Introducing a new kernel boot option:
amd_iommu=irtcachedis
which disables IRTE caching by setting the IRTCachedis bit in each IOMMU
Control register, and bypass the IRT invalidation process.
Co-developed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
[Awaiting sign-off by Alejandro]
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
---
.../admin-guide/kernel-parameters.txt | 1 +
drivers/iommu/amd/amd_iommu_types.h | 4 +++
drivers/iommu/amd/init.c | 36 +++++++++++++++++++
3 files changed, 41 insertions(+)
Comments
Hi Suravee,
On 5/18/2023 8:55 PM, Suravee Suthikulpanit wrote:
> An Interrupt Remapping Table (IRT) stores interrupt remapping configuration
> for each device. In a normal operation, the AMD IOMMU caches the table
> to optimize subsequent data accesses. This requires the IOMMU driver to
> invalidate IRT whenever it updates the table. The invalidation process
> includes issuing an INVALIDATE_INTERRUPT_TABLE command following by
> a COMPLETION_WAIT command.
>
> However, there are cases in which the IRT is updated at a high rate.
> For example, for IOMMU AVIC, the IRTE[IsRun] bit is updated on every
> vcpu scheduling (i.e. amd_iommu_update_ga()). On system with large
> amount of vcpus and VFIO PCI pass-through devices, the invalidation
> process could potentially become a performance bottleneck.
>
> Introducing a new kernel boot option:
>
> amd_iommu=irtcachedis
>
> which disables IRTE caching by setting the IRTCachedis bit in each IOMMU
> Control register, and bypass the IRT invalidation process.
>
> Co-developed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
> [Awaiting sign-off by Alejandro]
Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com
I sanity tested the kdump mechanism, and confirmed that
CONTROL_IRTCACHEDIS is set appropriately based on the irtcachedis kernel
parameter.
Also, I have not observed any errors during multiple rounds of testing
with large vCPU counts and VFIO passthrough devices under
interrupt-intensive workload that causes heavy vCPU scheduling activity
and exercises the relevant code path.
Thank you,
Alejandro
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
> .../admin-guide/kernel-parameters.txt | 1 +
> drivers/iommu/amd/amd_iommu_types.h | 4 +++
> drivers/iommu/amd/init.c | 36 +++++++++++++++++++
> 3 files changed, 41 insertions(+)
>
>
On Thu, May 18, 2023 at 08:55:27PM -0400, Suravee Suthikulpanit wrote:
> An Interrupt Remapping Table (IRT) stores interrupt remapping configuration
> for each device. In a normal operation, the AMD IOMMU caches the table
> to optimize subsequent data accesses. This requires the IOMMU driver to
> invalidate IRT whenever it updates the table. The invalidation process
> includes issuing an INVALIDATE_INTERRUPT_TABLE command following by
> a COMPLETION_WAIT command.
>
> However, there are cases in which the IRT is updated at a high rate.
> For example, for IOMMU AVIC, the IRTE[IsRun] bit is updated on every
> vcpu scheduling (i.e. amd_iommu_update_ga()). On system with large
> amount of vcpus and VFIO PCI pass-through devices, the invalidation
> process could potentially become a performance bottleneck.
>
> Introducing a new kernel boot option:
>
> amd_iommu=irtcachedis
>
> which disables IRTE caching by setting the IRTCachedis bit in each IOMMU
> Control register, and bypass the IRT invalidation process.
>
> Co-developed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
> [Awaiting sign-off by Alejandro]
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> ---
> .../admin-guide/kernel-parameters.txt | 1 +
> drivers/iommu/amd/amd_iommu_types.h | 4 +++
> drivers/iommu/amd/init.c | 36 +++++++++++++++++++
> 3 files changed, 41 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 6221a1d057dd..f29dee600faf 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -323,6 +323,7 @@
> option with care.
> pgtbl_v1 - Use v1 page table for DMA-API (Default).
> pgtbl_v2 - Use v2 page table for DMA-API.
> + irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
>
> amd_iommu_dump= [HW,X86-64]
> Enable AMD IOMMU driver option to dump the ACPI table
> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
> index a0ff1e852efc..486a052e37ca 100644
> --- a/drivers/iommu/amd/amd_iommu_types.h
> +++ b/drivers/iommu/amd/amd_iommu_types.h
> @@ -172,6 +172,7 @@
> #define CONTROL_GAINT_EN 29
> #define CONTROL_XT_EN 50
> #define CONTROL_INTCAPXT_EN 51
> +#define CONTROL_IRTCACHEDIS 59
> #define CONTROL_SNPAVIC_EN 61
>
> #define CTRL_INV_TO_MASK (7 << CONTROL_INV_TIMEOUT)
> @@ -708,6 +709,9 @@ struct amd_iommu {
> /* if one, we need to send a completion wait command */
> bool need_sync;
>
> + /* true if disable irte caching */
> + bool irtcachedis_enabled;
> +
> /* Handle for IOMMU core code */
> struct iommu_device iommu;
>
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index fd487c33b28a..fc0392d706db 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -160,6 +160,7 @@ static int amd_iommu_xt_mode = IRQ_REMAP_XAPIC_MODE;
> static bool amd_iommu_detected;
> static bool amd_iommu_disabled __initdata;
> static bool amd_iommu_force_enable __initdata;
> +static bool amd_iommu_irtcachedis;
> static int amd_iommu_target_ivhd_type;
>
> /* Global EFR and EFR2 registers */
> @@ -477,6 +478,9 @@ static void iommu_disable(struct amd_iommu *iommu)
>
> /* Disable IOMMU hardware itself */
> iommu_feature_disable(iommu, CONTROL_IOMMU_EN);
> +
> + /* Clear IRTE cache disabling bit */
> + iommu_feature_disable(iommu, CONTROL_IRTCACHEDIS);
> }
>
> /*
> @@ -2700,6 +2704,33 @@ static void iommu_enable_ga(struct amd_iommu *iommu)
> #endif
> }
>
> +static void iommu_disable_irtcachedis(struct amd_iommu *iommu)
> +{
> + iommu_feature_disable(iommu, CONTROL_IRTCACHEDIS);
> +}
> +
> +static void iommu_enable_irtcachedis(struct amd_iommu *iommu)
> +{
> + u64 ctrl;
> +
> + if (!amd_iommu_irtcachedis)
> + return;
> +
> + /*
> + * Note:
> + * The support for IRTCacheDis feature is dertermined by
> + * checking if the bit is writable.
> + */
> + iommu_feature_enable(iommu, CONTROL_IRTCACHEDIS);
> + ctrl = readq(iommu->mmio_base + MMIO_CONTROL_OFFSET);
> + ctrl &= (1ULL << CONTROL_IRTCACHEDIS);
> + if (ctrl)
> + iommu->irtcachedis_enabled = true;
> + pr_info("iommu%d (%#06x) : IRT cache is %s\n",
> + iommu->index, iommu->devid,
> + iommu->irtcachedis_enabled ? "disabled" : "enabled");
> +}
> +
> static void early_enable_iommu(struct amd_iommu *iommu)
> {
> iommu_disable(iommu);
> @@ -2710,6 +2741,7 @@ static void early_enable_iommu(struct amd_iommu *iommu)
> iommu_set_exclusion_range(iommu);
> iommu_enable_ga(iommu);
> iommu_enable_xt(iommu);
> + iommu_enable_irtcachedis(iommu);
> iommu_enable(iommu);
> iommu_flush_all_caches(iommu);
> }
> @@ -2760,10 +2792,12 @@ static void early_enable_iommus(void)
> for_each_iommu(iommu) {
> iommu_disable_command_buffer(iommu);
> iommu_disable_event_buffer(iommu);
> + iommu_disable_irtcachedis(iommu);
> iommu_enable_command_buffer(iommu);
> iommu_enable_event_buffer(iommu);
> iommu_enable_ga(iommu);
> iommu_enable_xt(iommu);
> + iommu_enable_irtcachedis(iommu);
> iommu_set_device_table(iommu);
> iommu_flush_all_caches(iommu);
> }
> @@ -3411,6 +3445,8 @@ static int __init parse_amd_iommu_options(char *str)
> amd_iommu_pgtable = AMD_IOMMU_V1;
> } else if (strncmp(str, "pgtbl_v2", 8) == 0) {
> amd_iommu_pgtable = AMD_IOMMU_V2;
> + } else if (strncmp(str, "irtcachedis", 11) == 0) {
> + amd_iommu_irtcachedis = true;
> } else {
> pr_notice("Unknown option - '%s'\n", str);
> }
> --
> 2.31.1
>
@@ -323,6 +323,7 @@
option with care.
pgtbl_v1 - Use v1 page table for DMA-API (Default).
pgtbl_v2 - Use v2 page table for DMA-API.
+ irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
amd_iommu_dump= [HW,X86-64]
Enable AMD IOMMU driver option to dump the ACPI table
@@ -172,6 +172,7 @@
#define CONTROL_GAINT_EN 29
#define CONTROL_XT_EN 50
#define CONTROL_INTCAPXT_EN 51
+#define CONTROL_IRTCACHEDIS 59
#define CONTROL_SNPAVIC_EN 61
#define CTRL_INV_TO_MASK (7 << CONTROL_INV_TIMEOUT)
@@ -708,6 +709,9 @@ struct amd_iommu {
/* if one, we need to send a completion wait command */
bool need_sync;
+ /* true if disable irte caching */
+ bool irtcachedis_enabled;
+
/* Handle for IOMMU core code */
struct iommu_device iommu;
@@ -160,6 +160,7 @@ static int amd_iommu_xt_mode = IRQ_REMAP_XAPIC_MODE;
static bool amd_iommu_detected;
static bool amd_iommu_disabled __initdata;
static bool amd_iommu_force_enable __initdata;
+static bool amd_iommu_irtcachedis;
static int amd_iommu_target_ivhd_type;
/* Global EFR and EFR2 registers */
@@ -477,6 +478,9 @@ static void iommu_disable(struct amd_iommu *iommu)
/* Disable IOMMU hardware itself */
iommu_feature_disable(iommu, CONTROL_IOMMU_EN);
+
+ /* Clear IRTE cache disabling bit */
+ iommu_feature_disable(iommu, CONTROL_IRTCACHEDIS);
}
/*
@@ -2700,6 +2704,33 @@ static void iommu_enable_ga(struct amd_iommu *iommu)
#endif
}
+static void iommu_disable_irtcachedis(struct amd_iommu *iommu)
+{
+ iommu_feature_disable(iommu, CONTROL_IRTCACHEDIS);
+}
+
+static void iommu_enable_irtcachedis(struct amd_iommu *iommu)
+{
+ u64 ctrl;
+
+ if (!amd_iommu_irtcachedis)
+ return;
+
+ /*
+ * Note:
+ * The support for IRTCacheDis feature is dertermined by
+ * checking if the bit is writable.
+ */
+ iommu_feature_enable(iommu, CONTROL_IRTCACHEDIS);
+ ctrl = readq(iommu->mmio_base + MMIO_CONTROL_OFFSET);
+ ctrl &= (1ULL << CONTROL_IRTCACHEDIS);
+ if (ctrl)
+ iommu->irtcachedis_enabled = true;
+ pr_info("iommu%d (%#06x) : IRT cache is %s\n",
+ iommu->index, iommu->devid,
+ iommu->irtcachedis_enabled ? "disabled" : "enabled");
+}
+
static void early_enable_iommu(struct amd_iommu *iommu)
{
iommu_disable(iommu);
@@ -2710,6 +2741,7 @@ static void early_enable_iommu(struct amd_iommu *iommu)
iommu_set_exclusion_range(iommu);
iommu_enable_ga(iommu);
iommu_enable_xt(iommu);
+ iommu_enable_irtcachedis(iommu);
iommu_enable(iommu);
iommu_flush_all_caches(iommu);
}
@@ -2760,10 +2792,12 @@ static void early_enable_iommus(void)
for_each_iommu(iommu) {
iommu_disable_command_buffer(iommu);
iommu_disable_event_buffer(iommu);
+ iommu_disable_irtcachedis(iommu);
iommu_enable_command_buffer(iommu);
iommu_enable_event_buffer(iommu);
iommu_enable_ga(iommu);
iommu_enable_xt(iommu);
+ iommu_enable_irtcachedis(iommu);
iommu_set_device_table(iommu);
iommu_flush_all_caches(iommu);
}
@@ -3411,6 +3445,8 @@ static int __init parse_amd_iommu_options(char *str)
amd_iommu_pgtable = AMD_IOMMU_V1;
} else if (strncmp(str, "pgtbl_v2", 8) == 0) {
amd_iommu_pgtable = AMD_IOMMU_V2;
+ } else if (strncmp(str, "irtcachedis", 11) == 0) {
+ amd_iommu_irtcachedis = true;
} else {
pr_notice("Unknown option - '%s'\n", str);
}