RISC-V: Add support for sqoscfg CSR

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
from 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>

arch/riscv/Kconfig

@@ -409,6 +409,25 @@ 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 QoS 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 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_SVNAPOT
 	bool "Svnapot extension support for supervisor mode NAPOT pages"
 	depends on 64BIT && MMU

arch/riscv/include/asm/csr.h

@@ -59,6 +59,13 @@
 #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))
 
@@ -245,6 +252,7 @@
 #define CSR_STVAL		0x143
 #define CSR_SIP			0x144
 #define CSR_SATP		0x180
+#define CSR_SQOSCFG		0x181
 
 #define CSR_STIMECMP		0x14D
 #define CSR_STIMECMPH		0x15D

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 */

arch/riscv/include/asm/qos.h

+/* 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 */
+DECLARE_PER_CPU(u32, cpu_sqoscfg);
+
+static inline void __switch_to_sqoscfg(struct task_struct *prev,
+				       struct task_struct *next)
+{
+	u32 *cpu_sqoscfg_ptr = this_cpu_ptr(&cpu_sqoscfg);
+	u32 thread_sqoscfg;
+
+	thread_sqoscfg = READ_ONCE(next->thread.sqoscfg);
+
+	if (thread_sqoscfg != *cpu_sqoscfg_ptr) {
+		*cpu_sqoscfg_ptr = thread_sqoscfg;
+		csr_write(CSR_SQOSCFG, thread_sqoscfg);
+	}
+}
+
+static __always_inline bool has_sqoscfg(void)
+{
+	return riscv_has_extension_likely(RISCV_ISA_EXT_SSQOSID);
+}
+
+#else /* ! CONFIG_RISCV_ISA_SSQOSID  */
+
+static __always_inline bool has_sqoscfg(void) { return false; }
+#define __switch_to_sqoscfg(__prev, __next) do { } while (0)
+
+#endif /* CONFIG_RISCV_ISA_SSQOSID */
+
+#endif /* _ASM_RISCV_QOS_H */

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);
@@ -78,6 +79,8 @@ do {							\
 	struct task_struct *__next = (next);		\
 	if (has_fpu())					\
 		__switch_to_aux(__prev, __next);	\
+	if (has_sqoscfg())				\
+		__switch_to_sqoscfg(__prev, __next);	\
 	((last) = __switch_to(__prev, __next));		\
 } while (0)
 

arch/riscv/kernel/Makefile

@@ -89,3 +89,4 @@ obj-$(CONFIG_COMPAT)		+= compat_signal.o
 obj-$(CONFIG_COMPAT)		+= compat_vdso/
 
 obj-$(CONFIG_64BIT)		+= pi/
+obj-$(CONFIG_RISCV_ISA_SSQOSID) += qos/

arch/riscv/kernel/qos/Makefile

+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_RISCV_ISA_SSQOSID) += qos.o

arch/riscv/kernel/qos/qos.c

+// SPDX-License-Identifier: GPL-2.0-only
+#include <asm/qos.h>
+
+/* cached value of sqoscfg csr for each cpu */
+DEFINE_PER_CPU(u32, cpu_sqoscfg);