[RFC PATCH 02/21] RISC-V: Add support for sqoscfg CSR

[Drew Fustini <dfustini@baylibre.com>]

Add support for the sqoscfg CSR defined in the Ssqosid ISA extension
(Supervisor-mode Quality of Service ID). The CSR contains two fields:

  - Resource Control ID (RCID) used determine resource allocation
  - Monitoring Counter ID (MCID) used to track resource usage

Requests from a hart to shared resources like cache will be tagged with
these IDs. This allows the usage of shared resources to be associated
with the task currently running on the hart.

A sqoscfg field is added to thread_struct and has the same format as the
sqoscfg CSR. This allows the scheduler to set the hart's sqoscfg CSR to
contain the RCID and MCID for the task that is being scheduled in. The
sqoscfg CSR is only written to if the thread_struct.sqoscfg is different
than the current value of the CSR.

A per-cpu variable cpu_sqoscfg is used to mirror that state of the CSR.
This is because access to L1D hot memory should be several times faster
than a CSR read. Also, in the case of virtualization, accesses to this
CSR are trapped in the hypervisor.

Link: https://github.com/riscv-non-isa/riscv-cbqri/blob/main/riscv-cbqri.pdf
Co-developed-by: Kornel Dulęba <mindal@semihalf.com>
Signed-off-by: Kornel Dulęba <mindal@semihalf.com>
Signed-off-by: Drew Fustini <dfustini@baylibre.com>
---
Note:
- A version of this patch rebased on riscv/for-next was already
  submitted as an RFC to linux-riscv [1] with Message-ID:
    20230410043646.3138446-1-dfustini@baylibre.com
- This patch is included in this RFC series so as to provide a cohesive
  demonstration in one series.

[1] https://lore.kernel.org/lkml/20230410043646.3138446-1-dfustini@baylibre.com/

 arch/riscv/Kconfig                 | 19 ++++++++++++++
 arch/riscv/include/asm/csr.h       |  8 ++++++
 arch/riscv/include/asm/processor.h |  3 +++
 arch/riscv/include/asm/qos.h       | 40 ++++++++++++++++++++++++++++++
 arch/riscv/include/asm/switch_to.h |  2 ++
 5 files changed, 72 insertions(+)
 create mode 100644 arch/riscv/include/asm/qos.h

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index c5e42cc37604..9d4c8c505191 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -398,6 +398,25 @@ config RISCV_ISA_C
 
 	  If you don't know what to do here, say Y.
 
+config RISCV_ISA_SSQOSID
+	bool "Ssqosid extension support for supervisor mode Quality of Service ID"
+	default y
+	help
+	  Adds support for the Ssqosid ISA extension (Supervisor-mode
+	  Quality of Service ID).
+
+	  Ssqosid defines the sqoscfg CSR which allows the system to tag
+	  the running process with RCID (Resource Control ID) and MCID
+	  (Monitoring Counter ID). The RCID is used to determine resource
+	  allocation. The MCID is used to track resource usage in event
+	  counters.
+
+	  For example, a cache controller may use the RCID to apply a
+	  cache partitioning scheme and use the MCID to track how much
+	  cache a process, or a group of processes, is using.
+
+	  If you don't know what to do here, say Y.
+
 config RISCV_ISA_SVPBMT
 	bool "SVPBMT extension support"
 	depends on 64BIT && MMU
diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
index 0e571f6483d9..ab222ca15799 100644
--- a/arch/riscv/include/asm/csr.h
+++ b/arch/riscv/include/asm/csr.h
@@ -60,6 +60,13 @@
 #define SATP_ASID_MASK	_AC(0xFFFF, UL)
 #endif
 
+/* SQOSCFG fields */
+#define SQOSCFG_RCID_MASK	_AC(0x00000FFF, UL)
+#define SQOSCFG_MCID_MASK	SQOSCFG_RCID_MASK
+#define SQOSCFG_MCID_SHIFT	16
+#define SQOSCFG_MASK		((SQOSCFG_MCID_MASK << SQOSCFG_MCID_SHIFT) | \
+				  SQOSCFG_RCID_MASK)
+
 /* Exception cause high bit - is an interrupt if set */
 #define CAUSE_IRQ_FLAG		(_AC(1, UL) << (__riscv_xlen - 1))
 
@@ -246,6 +253,7 @@
 #define CSR_STVAL		0x143
 #define CSR_SIP			0x144
 #define CSR_SATP		0x180
+#define CSR_SQOSCFG		0x181
 
 #define CSR_STIMECMP		0x14D
 #define CSR_STIMECMPH		0x15D
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 94a0590c6971..724b2aa2732d 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -39,6 +39,9 @@ struct thread_struct {
 	unsigned long s[12];	/* s[0]: frame pointer */
 	struct __riscv_d_ext_state fstate;
 	unsigned long bad_cause;
+#ifdef CONFIG_RISCV_ISA_SSQOSID
+	u32 sqoscfg;
+#endif
 };
 
 /* Whitelist the fstate from the task_struct for hardened usercopy */
diff --git a/arch/riscv/include/asm/qos.h b/arch/riscv/include/asm/qos.h
new file mode 100644
index 000000000000..297e7fb64d80
--- /dev/null
+++ b/arch/riscv/include/asm/qos.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RISCV_QOS_H
+#define _ASM_RISCV_QOS_H
+
+#ifdef CONFIG_RISCV_ISA_SSQOSID
+
+#include <linux/sched.h>
+#include <linux/jump_label.h>
+
+#include <asm/barrier.h>
+#include <asm/csr.h>
+#include <asm/hwcap.h>
+
+/* cached value of sqoscfg csr for each cpu */
+static DEFINE_PER_CPU(u32, cpu_sqoscfg);
+
+static void __qos_sched_in(struct task_struct *task)
+{
+	u32 *cpu_sqoscfg_ptr = this_cpu_ptr(&cpu_sqoscfg);
+	u32 thread_sqoscfg;
+
+	thread_sqoscfg = READ_ONCE(task->thread.sqoscfg);
+
+	if (thread_sqoscfg != *cpu_sqoscfg_ptr) {
+		*cpu_sqoscfg_ptr = thread_sqoscfg;
+		csr_write(CSR_SQOSCFG, thread_sqoscfg);
+	}
+}
+
+static inline void qos_sched_in(struct task_struct *task)
+{
+	if (riscv_has_extension_likely(RISCV_ISA_EXT_SSQOSID))
+		__qos_sched_in(task);
+}
+#else
+
+static inline void qos_sched_in(struct task_struct *task) {}
+
+#endif /* CONFIG_RISCV_ISA_SSQOSID */
+#endif /* _ASM_RISCV_QOS_H */
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index 60f8ca01d36e..75d9bfd766af 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -12,6 +12,7 @@
 #include <asm/processor.h>
 #include <asm/ptrace.h>
 #include <asm/csr.h>
+#include <asm/qos.h>
 
 #ifdef CONFIG_FPU
 extern void __fstate_save(struct task_struct *save_to);
@@ -79,6 +80,7 @@ do {							\
 	if (has_fpu())					\
 		__switch_to_aux(__prev, __next);	\
 	((last) = __switch_to(__prev, __next));		\
+	qos_sched_in(__next);				\
 } while (0)
 
 #endif /* _ASM_RISCV_SWITCH_TO_H */
-- 
2.34.1