linux-kernel - [PATCH v7 03/10] x86,fs/resctrl: Detect io

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Message-ID: <998f42d5c92cce9d7d83bcd54d25761242839b4a.1752167718.git.babu.moger@amd.com>
Date: Thu, 10 Jul 2025 12:16:17 -0500
From: Babu Moger <babu.moger@....com>
To: <corbet@....net>, <tony.luck@...el.com>, <reinette.chatre@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <akpm@...ux-foundation.org>,
	<paulmck@...nel.org>, <rostedt@...dmis.org>, <Neeraj.Upadhyay@....com>,
	<david@...hat.com>, <arnd@...db.de>, <fvdl@...gle.com>, <seanjc@...gle.com>,
	<thomas.lendacky@....com>, <pawan.kumar.gupta@...ux.intel.com>,
	<babu.moger@....com>, <yosry.ahmed@...ux.dev>, <sohil.mehta@...el.com>,
	<xin@...or.com>, <kai.huang@...el.com>, <xiaoyao.li@...el.com>,
	<peterz@...radead.org>, <me@...aill.net>, <mario.limonciello@....com>,
	<xin3.li@...el.com>, <ebiggers@...gle.com>, <ak@...ux.intel.com>,
	<chang.seok.bae@...el.com>, <andrew.cooper3@...rix.com>,
	<perry.yuan@....com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v7 03/10] x86,fs/resctrl: Detect io_alloc feature

Smart Data Cache Injection (SDCI) is a mechanism that enables direct
insertion of data from I/O devices into the L3 cache. It can reduce the
demands on DRAM bandwidth and reduces latency to the processor consuming
the I/O data.

Introduce cache resource property "io_alloc_capable" that an architecture
can set if a portion of the cache can be allocated for I/O traffic.

Set this property on x86 systems that support SDCIAE (L3 Smart Data Cache
Injection Allocation Enforcement). This property is set only for the L3
cache resource on systems that support SDCIAE.

Signed-off-by: Babu Moger <babu.moger@....com>
---
v7: Few text updates in changelog and resctrl.h.

v6: No changes.

v5: No changes.

v4: Updated the commit message and code comment based on feedback.

v3: Rewrote commit log. Changed the text to bit generic than the AMD specific.
    Renamed the rdt_get_sdciae_alloc_cfg() to rdt_set_io_alloc_capable().
    Removed leftover comment from v2.

v2: Changed sdciae_capable to io_alloc_capable to make it generic feature.
    Also moved the io_alloc_capable in struct resctrl_cache.
---
 arch/x86/kernel/cpu/resctrl/core.c | 7 +++++++
 include/linux/resctrl.h            | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index f6d84882cc4e..1d1002526745 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -274,6 +274,11 @@ static void rdt_get_cdp_config(int level)
 	rdt_resources_all[level].r_resctrl.cdp_capable = true;
 }
 
+static void rdt_set_io_alloc_capable(struct rdt_resource *r)
+{
+	r->cache.io_alloc_capable = true;
+}
+
 static void rdt_get_cdp_l3_config(void)
 {
 	rdt_get_cdp_config(RDT_RESOURCE_L3);
@@ -842,6 +847,8 @@ static __init bool get_rdt_alloc_resources(void)
 		rdt_get_cache_alloc_cfg(1, r);
 		if (rdt_cpu_has(X86_FEATURE_CDP_L3))
 			rdt_get_cdp_l3_config();
+		if (rdt_cpu_has(X86_FEATURE_SDCIAE))
+			rdt_set_io_alloc_capable(r);
 		ret = true;
 	}
 	if (rdt_cpu_has(X86_FEATURE_CAT_L2)) {
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 6fb4894b8cfd..010f238843b2 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -191,6 +191,8 @@ struct rdt_mon_domain {
  * @arch_has_sparse_bitmasks:	True if a bitmask like f00f is valid.
  * @arch_has_per_cpu_cfg:	True if QOS_CFG register for this cache
  *				level has CPU scope.
+ * @io_alloc_capable:	True if portion of the cache can be configured
+ *			for I/O traffic.
  */
 struct resctrl_cache {
 	unsigned int	cbm_len;
@@ -198,6 +200,7 @@ struct resctrl_cache {
 	unsigned int	shareable_bits;
 	bool		arch_has_sparse_bitmasks;
 	bool		arch_has_per_cpu_cfg;
+	bool		io_alloc_capable;
 };
 
 /**
-- 
2.34.1