"io_alloc" enables direct insertion of data from I/O devices into the
cache.
On AMD systems, "io_alloc" feature is backed by L3 Smart Data Cache
Injection Allocation Enforcement (SDCIAE). Change SDCIAE state by setting
(to enable) or clearing (to disable) bit 1 of MSR L3_QOS_EXT_CFG on all
logical processors within the cache domain.
Introduce architecture-specific call to enable and disable the feature.
The SDCIAE feature details are available in APM listed below [1].
[1] AMD64 Architecture Programmer's Manual Volume 2: System Programming
Publication # 24593 Revision 3.41 section 19.4.7 L3 Smart Data Cache
Injection Allocation Enforcement (SDCIAE)
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
Signed-off-by: Babu Moger <babu.moger@amd.com>
---
v7: Removed the inline for resctrl_arch_get_io_alloc_enabled().
Update code comment in resctrl.h.
Changed the subject to x86,fs/resctrl.
v6: Added lockdep_assert_cpus_held() in _resctrl_sdciae_enable() to protect
r->ctrl_domains.
Added more comments in include/linux/resctrl.h.
v5: Resolved conflicts due to recent resctrl FS/ARCH code restructure.
The files monitor.c/rdtgroup.c have been split between FS and ARCH directories.
Moved prototypes of resctrl_arch_io_alloc_enable() and
resctrl_arch_get_io_alloc_enabled() to include/linux/resctrl.h.
v4: Updated the commit log to address the feedback.
v3: Passed the struct rdt_resource to resctrl_arch_get_io_alloc_enabled() instead of resource id.
Renamed the _resctrl_io_alloc_enable() to _resctrl_sdciae_enable() as it is arch specific.
Changed the return to void in _resctrl_sdciae_enable() instead of int.
Added more context in commit log and fixed few typos.
v2: Renamed the functions to simplify the code.
Renamed sdciae_capable to io_alloc_capable.
Changed the name of few arch functions similar to ABMC series.
resctrl_arch_get_io_alloc_enabled()
resctrl_arch_io_alloc_enable()
---
arch/x86/include/asm/msr-index.h | 1 +
arch/x86/kernel/cpu/resctrl/internal.h | 5 ++++
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 40 ++++++++++++++++++++++++++
include/linux/resctrl.h | 21 ++++++++++++++
4 files changed, 67 insertions(+)
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 7490bb5c0776..c998cf0e1375 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -1222,6 +1222,7 @@
/* - AMD: */
#define MSR_IA32_MBA_BW_BASE 0xc0000200
#define MSR_IA32_SMBA_BW_BASE 0xc0000280
+#define MSR_IA32_L3_QOS_EXT_CFG 0xc00003ff
#define MSR_IA32_EVT_CFG_BASE 0xc0000400
/* AMD-V MSRs */
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 5e3c41b36437..70f5317f1ce4 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -37,6 +37,9 @@ struct arch_mbm_state {
u64 prev_msr;
};
+/* Setting bit 1 in L3_QOS_EXT_CFG enables the SDCIAE feature. */
+#define SDCIAE_ENABLE_BIT 1
+
/**
* struct rdt_hw_ctrl_domain - Arch private attributes of a set of CPUs that share
* a resource for a control function
@@ -102,6 +105,7 @@ struct msr_param {
* @mon_scale: cqm counter * mon_scale = occupancy in bytes
* @mbm_width: Monitor width, to detect and correct for overflow.
* @cdp_enabled: CDP state of this resource
+ * @sdciae_enabled: SDCIAE feature (backing "io_alloc") is enabled.
*
* Members of this structure are either private to the architecture
* e.g. mbm_width, or accessed via helpers that provide abstraction. e.g.
@@ -115,6 +119,7 @@ struct rdt_hw_resource {
unsigned int mon_scale;
unsigned int mbm_width;
bool cdp_enabled;
+ bool sdciae_enabled;
};
static inline struct rdt_hw_resource *resctrl_to_arch_res(struct rdt_resource *r)
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 885026468440..c165ac333336 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -229,6 +229,46 @@ bool resctrl_arch_get_cdp_enabled(enum resctrl_res_level l)
return rdt_resources_all[l].cdp_enabled;
}
+bool resctrl_arch_get_io_alloc_enabled(struct rdt_resource *r)
+{
+ return resctrl_to_arch_res(r)->sdciae_enabled;
+}
+
+static void resctrl_sdciae_set_one_amd(void *arg)
+{
+ bool *enable = arg;
+
+ if (*enable)
+ msr_set_bit(MSR_IA32_L3_QOS_EXT_CFG, SDCIAE_ENABLE_BIT);
+ else
+ msr_clear_bit(MSR_IA32_L3_QOS_EXT_CFG, SDCIAE_ENABLE_BIT);
+}
+
+static void _resctrl_sdciae_enable(struct rdt_resource *r, bool enable)
+{
+ struct rdt_ctrl_domain *d;
+
+ /* Walking r->ctrl_domains, ensure it can't race with cpuhp */
+ lockdep_assert_cpus_held();
+
+ /* Update L3_QOS_EXT_CFG MSR on all the CPUs in all domains */
+ list_for_each_entry(d, &r->ctrl_domains, hdr.list)
+ on_each_cpu_mask(&d->hdr.cpu_mask, resctrl_sdciae_set_one_amd, &enable, 1);
+}
+
+int resctrl_arch_io_alloc_enable(struct rdt_resource *r, bool enable)
+{
+ struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
+
+ if (hw_res->r_resctrl.cache.io_alloc_capable &&
+ hw_res->sdciae_enabled != enable) {
+ _resctrl_sdciae_enable(r, enable);
+ hw_res->sdciae_enabled = enable;
+ }
+
+ return 0;
+}
+
void resctrl_arch_reset_all_ctrls(struct rdt_resource *r)
{
struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 010f238843b2..d98933ce77af 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -531,6 +531,27 @@ void resctrl_arch_reset_rmid_all(struct rdt_resource *r, struct rdt_mon_domain *
*/
void resctrl_arch_reset_all_ctrls(struct rdt_resource *r);
+/**
+ * resctrl_arch_io_alloc_enable() - Enable/disable io_alloc feature.
+ * @r: The resctrl resource.
+ * @enable: Enable (true) or disable (false) io_alloc on resource @r.
+ *
+ * This can be called from any CPU.
+ *
+ * Return:
+ * 0 on success, <0 on error.
+ */
+int resctrl_arch_io_alloc_enable(struct rdt_resource *r, bool enable);
+
+/**
+ * resctrl_arch_get_io_alloc_enabled() - Get io_alloc feature state.
+ * @r: The resctrl resource.
+ *
+ * Return:
+ * true if io_alloc is enabled or false if disabled.
+ */
+bool resctrl_arch_get_io_alloc_enabled(struct rdt_resource *r);
+
extern unsigned int resctrl_rmid_realloc_threshold;
extern unsigned int resctrl_rmid_realloc_limit;
--
2.34.1Hi Babu, On 7/10/25 10:16 AM, Babu Moger wrote: > "io_alloc" enables direct insertion of data from I/O devices into the > cache. > > On AMD systems, "io_alloc" feature is backed by L3 Smart Data Cache > Injection Allocation Enforcement (SDCIAE). Change SDCIAE state by setting > (to enable) or clearing (to disable) bit 1 of MSR L3_QOS_EXT_CFG on all > logical processors within the cache domain. > > Introduce architecture-specific call to enable and disable the feature. > > The SDCIAE feature details are available in APM listed below [1]. > [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming > Publication # 24593 Revision 3.41 section 19.4.7 L3 Smart Data Cache > Injection Allocation Enforcement (SDCIAE) > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 > Signed-off-by: Babu Moger <babu.moger@amd.com> > --- ... > > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > index 885026468440..c165ac333336 100644 > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c The code looks good to me but rdtgroup.c is becoming bloated by being the default place for any resctrl changes. While I do know there are counter examples (and I admit I do not have a clear understanding of original intent) ctrlmondata.c is documented and supported by its content as the place for cache allocation code. Could you please move these changes to arch/x86/kernel/cpu/resctrl/ctrlmondata.c? I will try to highlight the other places where I believe the either fs/resctrl/ctrlmondata.c or arch/x86/kernel/cpu/resctrl/ctrlmondata.c is more appropriate but please as a high level consider where appropriate to move the IO alloc code to be with the rest of the cache allocation code. Looking at the series it will help keep a couple of existing static functions static and keep data structures local to cache allocation code. Reinette
On 7/21/25 18:32, Reinette Chatre wrote: > Hi Babu, > > On 7/10/25 10:16 AM, Babu Moger wrote: >> "io_alloc" enables direct insertion of data from I/O devices into the >> cache. >> >> On AMD systems, "io_alloc" feature is backed by L3 Smart Data Cache >> Injection Allocation Enforcement (SDCIAE). Change SDCIAE state by setting >> (to enable) or clearing (to disable) bit 1 of MSR L3_QOS_EXT_CFG on all >> logical processors within the cache domain. >> >> Introduce architecture-specific call to enable and disable the feature. >> >> The SDCIAE feature details are available in APM listed below [1]. >> [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming >> Publication # 24593 Revision 3.41 section 19.4.7 L3 Smart Data Cache >> Injection Allocation Enforcement (SDCIAE) >> >> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 >> Signed-off-by: Babu Moger <babu.moger@amd.com> >> --- > > ... > >> >> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> index 885026468440..c165ac333336 100644 >> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c >> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > > The code looks good to me but rdtgroup.c is becoming bloated by being the default place for > any resctrl changes. While I do know there are counter examples (and I admit I do > not have a clear understanding of original intent) ctrlmondata.c is documented and supported > by its content as the place for cache allocation code. Could you please move these changes > to arch/x86/kernel/cpu/resctrl/ctrlmondata.c? I will try to highlight the other places where > I believe the either fs/resctrl/ctrlmondata.c or arch/x86/kernel/cpu/resctrl/ctrlmondata.c is > more appropriate but please as a high level consider where appropriate to move the IO alloc > code to be with the rest of the cache allocation code. Looking at the series it will help keep > a couple of existing static functions static and keep data structures local to cache allocation > code. > Sure. Moved it to arch/x86/kernel/cpu/resctrl/ctrlmondata.c. -- Thanks Babu Moger
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