[v1,4/6] xen/riscv: introduce cache management operations (CMO)

Commit Message

Oleksii Kurochko Nov. 27, 2024, 12:50 p.m. UTC

KConfig HAS_CMO is introduced to handle if the platform has CMO related
extenstions ( such as Zicbom, Zicboz, Zicbop etc ) or not.

if HAS_CMO isn't set stubs for clean_and_invalidate_dcache_va_range()
and clean_dcache_va_range() are implemented as just returning
-EOPNOTSUPP.

Our current platform is QEMU which doesn't model caches so it should be
fine to follow implementations when HAS_CMO isn't set.

invalidate_icache() is implemented using fence.i instruction as
mentioned in the unpriv spec:
  The FENCE.I instruction was designed to support a wide variety of
  implementations. A simple implementation can flush the local instruction
  cache and the instruction pipeline when the FENCE.I is executed.
  A more complex implementation might snoop the instruction (data) cache
  on every data (instruction) cache miss, or use an inclusive unified
  private L2 cache to invalidate lines from the primary instruction cache
  when they are being written by a local store instruction.
  If instruction and data caches are kept coherent in this way, or if the
  memory system consists of only uncached RAMs, then just the fetch pipeline
  needs to be flushed at a FENCE.I.

Signed-off-by: Oleksii Kurochko <[e-mail]>
---
 xen/arch/riscv/Kconfig            |  3 +++
 xen/arch/riscv/include/asm/page.h | 18 +++++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

Patch

diff --git a/xen/arch/riscv/Kconfig b/xen/arch/riscv/Kconfig
index 1858004676..4f1fcfd21a 100644
--- a/xen/arch/riscv/Kconfig
+++ b/xen/arch/riscv/Kconfig
@@ -14,6 +14,9 @@  config ARCH_DEFCONFIG
 	string
 	default "arch/riscv/configs/tiny64_defconfig"
 
+config HAS_CMO # Cache Management Operations
+	bool
+
 menu "Architecture Features"
 
 source "arch/Kconfig"
diff --git a/xen/arch/riscv/include/asm/page.h b/xen/arch/riscv/include/asm/page.h
index bf3f75e85d..0f297141d3 100644
--- a/xen/arch/riscv/include/asm/page.h
+++ b/xen/arch/riscv/include/asm/page.h
@@ -7,6 +7,7 @@ 
 
 #include <xen/bug.h>
 #include <xen/const.h>
+#include <xen/errno.h>
 #include <xen/types.h>
 
 #include <asm/atomic.h>
@@ -148,9 +149,24 @@  static inline bool pte_is_mapping(pte_t p)
     return (p.pte & PTE_VALID) && (p.pte & PTE_ACCESS_MASK);
 }
 
+#ifndef HAS_CMO
+static inline int clean_and_invalidate_dcache_va_range(const void *p, unsigned long size)
+{
+    return -EOPNOTSUPP;
+}
+
+static inline int clean_dcache_va_range(const void *p, unsigned long size)
+{
+    return -EOPNOTSUPP;
+}
+#else
+int clean_and_invalidate_dcache_va_range(const void *p, unsigned long size);
+int clean_dcache_va_range(const void *p, unsigned long size);
+#endif
+
 static inline void invalidate_icache(void)
 {
-    BUG_ON("unimplemented");
+    asm volatile ( "fence.i" ::: "memory" );
 }
 
 #define clear_page(page) memset((void *)(page), 0, PAGE_SIZE)