> -----Original Message-----
> From: Nathan Chen <[email protected]>
> Sent: 12 May 2026 20:35
> To: [email protected]; [email protected]
> Cc: Eric Auger <[email protected]>; Peter Maydell
> <[email protected]>; Philippe Mathieu-Daudé <[email protected]>;
> Zhao Liu <[email protected]>; Matt Ochs <[email protected]>; Nicolin
> Chen <[email protected]>; Shameer Kolothum Thodi
> <[email protected]>; Nathan Chen <[email protected]>
> Subject: [PATCH v3 4/7] hw/arm/smmuv3-accel: Implement "auto" value for
> "ssidsize"
>
> From: Nathan Chen <[email protected]>
>
> Allow accelerated SMMUv3 SSID size property to be derived from host
> IOMMU capabilities. Derive host values using IOMMU_GET_HW_INFO,
> retrieving SSID size from IDR1. When the auto SSID size is resolved
> to a non-zero value, PASID capability is advertised to the vIOMMU
> and accelerated use cases such as Shared Virtual Addressing (SVA)
> are supported.
>
> Reviewed-by: Eric Auger <[email protected]>
> Signed-off-by: Nathan Chen <[email protected]>
> ---
> hw/arm/smmuv3-accel.c | 18 ++++++++++++++++--
> hw/arm/smmuv3.c | 20 ++++++++++----------
> 2 files changed, 26 insertions(+), 12 deletions(-)
>
> diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
> index a5973bd499..5b1af062ee 100644
> --- a/hw/arm/smmuv3-accel.c
> +++ b/hw/arm/smmuv3-accel.c
> @@ -62,6 +62,12 @@ static void
> smmuv3_accel_auto_finalise(SMMUv3State *s,
> FIELD_EX32(info->idr[3], IDR3, RIL));
> }
>
> + if (s->ssidsize == SSID_SIZE_MODE_AUTO) {
> + /* Store for get_viommu_flags() to determine PASID support */
> + s->idr[1] = FIELD_DP32(s->idr[1], IDR1, SSIDSIZE,
> + FIELD_EX32(info->idr[1], IDR1, SSIDSIZE));
Nit: Not sure that comment makes sense. We need to update it
anyway, right?
> + }
> +
> accel->auto_finalised = true;
> }
>
> @@ -822,6 +828,13 @@ static AddressSpace
> *smmuv3_accel_find_add_as(PCIBus *bus, void *opaque,
> }
> }
>
> +static inline bool smmuv3_pasid_supported(SMMUv3State *s)
> +{
> + return s->ssidsize > SSID_SIZE_MODE_0 ||
> + (s->ssidsize == SSID_SIZE_MODE_AUTO &&
> + FIELD_EX32(s->idr[1], IDR1, SSIDSIZE));
> +}
> +
> static uint64_t smmuv3_accel_get_viommu_flags(void *opaque)
> {
> /*
> @@ -834,7 +847,7 @@ static uint64_t
> smmuv3_accel_get_viommu_flags(void *opaque)
> SMMUState *bs = opaque;
> SMMUv3State *s = ARM_SMMUV3(bs);
>
> - if (s->ssidsize > SSID_SIZE_MODE_0) {
> + if (smmuv3_pasid_supported(s)) {
> flags |= VIOMMU_FLAG_PASID_SUPPORTED;
> }
> return flags;
> @@ -975,7 +988,8 @@ bool smmuv3_accel_init(SMMUv3State *s, Error
> **errp)
> smmuv3_accel_as_init(s);
>
> if (s->ats == ON_OFF_AUTO_AUTO ||
> - s->ril == ON_OFF_AUTO_AUTO) {
> + s->ril == ON_OFF_AUTO_AUTO ||
> + s->ssidsize == SSID_SIZE_MODE_AUTO) {
> s->s_accel->auto_mode = true;
> }
>
> diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
> index 7ec4241ecf..cd30275717 100644
> --- a/hw/arm/smmuv3.c
> +++ b/hw/arm/smmuv3.c
> @@ -626,7 +626,10 @@ static int decode_ste(SMMUv3State *s,
> SMMUTransCfg *cfg,
> }
>
> /* Multiple context descriptors require SubstreamID support */
> - if (s->ssidsize == SSID_SIZE_MODE_0 && STE_S1CDMAX(ste) != 0) {
> + if ((s->ssidsize == SSID_SIZE_MODE_0 ||
> + (s->ssidsize == SSID_SIZE_MODE_AUTO &&
> + !FIELD_EX32(s->idr[1], IDR1, SSIDSIZE))) &&
> + STE_S1CDMAX(ste) != 0) {
> qemu_log_mask(LOG_UNIMP,
> "SMMUv3: multiple S1 context descriptors require SubstreamID
> support. "
> "Configure ssidsize > 0 (requires accel=on)\n");
> @@ -1965,10 +1968,6 @@ static void smmu_reset_exit(Object *obj,
> ResetType type)
>
> static bool smmu_validate_property(SMMUv3State *s, Error **errp)
> {
> - if (s->ssidsize == SSID_SIZE_MODE_AUTO) {
> - error_setg(errp, "ssidsize auto mode is not supported");
> - return false;
> - }
> if (s->oas != OAS_MODE_44 && s->oas != OAS_MODE_48) {
> error_setg(errp, "QEMU SMMUv3 model only implements 44 and 48 bit"
> "OAS; other OasMode values are not supported");
> @@ -1989,7 +1988,8 @@ static bool
> smmu_validate_property(SMMUv3State *s, Error **errp)
> return false;
> }
> if (s->ssidsize > SSID_SIZE_MODE_0) {
> - error_setg(errp, "ssidsize can only be set if accel=on");
> + error_setg(errp, "ssidsize can only be greater than 0 "
> + "bits if accel=on");
> return false;
> }
> return true;
> @@ -2173,11 +2173,11 @@ static void smmuv3_class_init(ObjectClass
> *klass, const void *data)
> "are 44 or 48 bits. Defaults to 44 bits. oas=auto is not "
> "supported.");
> object_class_property_set_description(klass, "ssidsize",
> - "Number of bits used to represent SubstreamIDs (SSIDs). "
> + "Set number of bits used to represent SubstreamIDs (SSIDs). "
> + "Valid values are 0-20 and auto. Defaults to 0. "
> "A value of N allows SSIDs in the range [0 .. 2^N - 1]. "
> - "Valid range is 0-20, where 0 disables SubstreamID support. "
> - "Defaults to 0. A value greater than 0 is required to enable "
> - "PASID support. ssidsize=auto is not supported.");
> + "A value of 0 disables SubstreamID support. A value greater "
> + "than 0 is required to enable PASID support.");
> }
>
> static int smmuv3_notify_flag_changed(IOMMUMemoryRegion *iommu,
Reviewed-by: Shameer Kolothum <[email protected]>
Thanks,
Shameer
