[PATCH -fixes v3 2/2] riscv: Save/restore envcfg CSR during CPU suspend

[Samuel Holland <samuel.holland@sifive.com>]

The value of the [ms]envcfg CSR is lost when entering a nonretentive
idle state, so the CSR must be rewritten when resuming the CPU.

The [ms]envcfg CSR was added in version 1.12 of the privileged ISA, and
is used by extensions other than Zicboz. However, the kernel currenly
has no way to determine the privileged ISA version. Since Zicboz is the
only in-kernel user of this CSR so far, use it as a proxy for
determining if the CSR is implemented.

Cc: <stable@vger.kernel.org> # v6.7+
Fixes: 43c16d51a19b ("RISC-V: Enable cbo.zero in usermode")
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

Changes in v3:
 - Check for Zicboz instead of the privileged ISA version

Changes in v2:
 - Check for privileged ISA v1.12 instead of the specific CSR
 - Use riscv_has_extension_likely() instead of new ALTERNATIVE()s

 arch/riscv/include/asm/suspend.h | 1 +
 arch/riscv/kernel/suspend.c      | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
index 02f87867389a..491296a335d0 100644
--- a/arch/riscv/include/asm/suspend.h
+++ b/arch/riscv/include/asm/suspend.h
@@ -14,6 +14,7 @@ struct suspend_context {
 	struct pt_regs regs;
 	/* Saved and restored by high-level functions */
 	unsigned long scratch;
+	unsigned long envcfg;
 	unsigned long tvec;
 	unsigned long ie;
 #ifdef CONFIG_MMU
diff --git a/arch/riscv/kernel/suspend.c b/arch/riscv/kernel/suspend.c
index 239509367e42..28166006688e 100644
--- a/arch/riscv/kernel/suspend.c
+++ b/arch/riscv/kernel/suspend.c
@@ -15,6 +15,8 @@
 void suspend_save_csrs(struct suspend_context *context)
 {
 	context->scratch = csr_read(CSR_SCRATCH);
+	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICBOZ))
+		context->envcfg = csr_read(CSR_ENVCFG);
 	context->tvec = csr_read(CSR_TVEC);
 	context->ie = csr_read(CSR_IE);
 
@@ -36,6 +38,8 @@ void suspend_save_csrs(struct suspend_context *context)
 void suspend_restore_csrs(struct suspend_context *context)
 {
 	csr_write(CSR_SCRATCH, context->scratch);
+	if (riscv_cpu_has_extension_unlikely(smp_processor_id(), RISCV_ISA_EXT_ZICBOZ))
+		csr_write(CSR_ENVCFG, context->envcfg);
 	csr_write(CSR_TVEC, context->tvec);
 	csr_write(CSR_IE, context->ie);
 
-- 
2.43.0