[PATCH] xen/riscv: copy_to_guest/copy_from_guest functionality.

[Milan Djokic <milandjokic1995@xxxxxxxxx>]

From: Slavisa Petrovic <Slavisa.Petrovic@xxxxxxxxx>

This patch implements copy_to_guest/copy_from_guest functions for RISC-V.
These functions are designed to facilitate data exchange between guest and 
hypervisor.

Signed-off-by: Milan Djokic <Milan.Djokic@xxxxxxxxx>
Signed-off-by: Slavisa Petrovic <Slavisa.Petrovic@xxxxxxxxx>
---
Tested on qemu with xcp-ng latest branch 
https://gitlab.com/xen-project/people/olkur/xen/-/merge_requests/6
Full description on how to setup test environment can be found in attached PR 
link (Linux kernel patching to support copy_from_guest/copy_to_guest for 
RISC-V).
Linux kernel patch shall be upstreamed after these changes are merged.
---
 xen/arch/riscv/Makefile                   |  1 +
 xen/arch/riscv/addr_translation.S         | 63 +++++++++++++++++++++++
 xen/arch/riscv/arch.mk                    |  6 ++-
 xen/arch/riscv/guestcopy.c                | 43 ++++++++++++++++
 xen/arch/riscv/include/asm/guest_access.h |  5 ++
 5 files changed, 117 insertions(+), 1 deletion(-)
 create mode 100644 xen/arch/riscv/addr_translation.S
 create mode 100644 xen/arch/riscv/guestcopy.c

diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
index a5eb2aed4b..1bd61cc993 100644
--- a/xen/arch/riscv/Makefile
+++ b/xen/arch/riscv/Makefile
@@ -10,6 +10,7 @@ obj-y += smp.o
 obj-y += stubs.o
 obj-y += traps.o
 obj-y += vm_event.o
+obj-y += addr_translation.o
 
 $(TARGET): $(TARGET)-syms
        $(OBJCOPY) -O binary -S $< $@
diff --git a/xen/arch/riscv/addr_translation.S 
b/xen/arch/riscv/addr_translation.S
new file mode 100644
index 0000000000..7e94774b47
--- /dev/null
+++ b/xen/arch/riscv/addr_translation.S
@@ -0,0 +1,63 @@
+#include <asm/riscv_encoding.h>
+#include <asm/asm.h>
+
+.macro add_extable lbl
+.pushsection .extable, "a"     /* Start .extable section */
+.balign      8                 /* Align to 8 bytes */
+.quad        \lbl              /* Add label address to extable */
+.popsection                    /* End section */
+.endm
+
+.section .text
+
+/*
+ * size_t _copy_to(uint64_t dest, const void *src, size_t len)
+ *
+ * a0 - dest
+ * a1 - src
+ * a2 - len
+ *
+ */
+
+.global _copy_to
+_copy_to:
+    la    t0, copy_done             /* Load address of return label */
+    mv    t2, zero                  /* Initialize counter to zero */
+loop_check:
+    beq   t2, a2, copy_done         /* Check if all bytes are copied */
+    lb    t3, (a1)                  /* Load byte from source (guest address) */
+store_byte:
+    hsv.b t3, (a0)                  /* Store byte to destination (host 
address) */
+    add_extable store_byte          /* Add exception table for this location */
+    addi  a0, a0, 1                 /* Increment destination pointer */
+    addi  a1, a1, 1                 /* Increment source pointer */
+    addi  t2, t2, 1                 /* Increment byte counter */
+    j     loop_check                /* Loop back if not done */
+
+/*
+ * size_t _copy_from(void *dest, uint64_t src, size_t len)
+ *
+ * a0 - dest
+ * a1 - src
+ * a2 - len
+ *
+ */
+
+.global _copy_from
+_copy_from:
+    la    t0, copy_done
+    mv    t2, zero
+loop_check_from:
+    beq   t2, a2, copy_done
+load_byte:
+    hlv.b t3, (a1)                  /* Load byte from guest address */
+    add_extable load_byte
+    sb    t3, (a0)
+    addi  a0, a0, 1
+    addi  a1, a1, 1
+    addi  t2, t2, 1
+    j     loop_check_from
+
+copy_done:
+    mv    a0, t2                    /* Return number of bytes copied */
+    ret
diff --git a/xen/arch/riscv/arch.mk b/xen/arch/riscv/arch.mk
index 17827c302c..f4098f5b5e 100644
--- a/xen/arch/riscv/arch.mk
+++ b/xen/arch/riscv/arch.mk
@@ -23,13 +23,17 @@ $(eval $(1) := \
        $(call as-insn,$(CC) $(riscv-generic-flags)_$(1),$(value 
$(1)-insn),_$(1)))
 endef
 
+h-extension-name := $(call cc-ifversion,-lt,1301, hh, h)
+$(h-extension-name)-insn := "hfence.gvma"
+$(call check-extension,$(h-extension-name))
+
 zbb-insn := "andn t0$(comma)t0$(comma)t0"
 $(call check-extension,zbb)
 
 zihintpause-insn := "pause"
 $(call check-extension,zihintpause)
 
-extensions := $(zbb) $(zihintpause)
+extensions := $(value $(h-extension-name)) $(zbb) $(zihintpause)
 
 extensions := $(subst $(space),,$(extensions))
 
diff --git a/xen/arch/riscv/guestcopy.c b/xen/arch/riscv/guestcopy.c
new file mode 100644
index 0000000000..0325956845
--- /dev/null
+++ b/xen/arch/riscv/guestcopy.c
@@ -0,0 +1,43 @@
+#include <xen/bug.h>
+#include <xen/domain_page.h>
+#include <xen/errno.h>
+#include <xen/sched.h>
+
+#include <asm/csr.h>
+#include <asm/guest_access.h>
+#include <asm/system.h>
+#include <asm/traps.h>
+
+unsigned long copy_to(uint64_t dest, void* src, size_t len)
+{
+    size_t bytes;
+
+    bytes = _copy_to(dest, src, len);
+
+    if (bytes == len)
+        return 0;
+    else
+        return -ENOSYS;
+}
+
+unsigned long copy_from(void *dest, uint64_t src, size_t len)
+{
+    size_t bytes;
+
+    bytes = _copy_from(dest, src, len);
+
+    if (bytes == len)
+        return 0;
+    else
+        return -ENOSYS;
+}
+
+unsigned long raw_copy_to_guest(void *to, const void *from, unsigned len)
+{
+    return copy_to((vaddr_t)to, (void *)from, len);
+}
+
+unsigned long raw_copy_from_guest(void *to, const void __user *from, unsigned 
len)
+{
+    return copy_from((void *)to, (vaddr_t)from, len);
+}
diff --git a/xen/arch/riscv/include/asm/guest_access.h 
b/xen/arch/riscv/include/asm/guest_access.h
index 7cd51fbbde..4fcf3fbf68 100644
--- a/xen/arch/riscv/include/asm/guest_access.h
+++ b/xen/arch/riscv/include/asm/guest_access.h
@@ -2,6 +2,11 @@
 #ifndef ASM__RISCV__GUEST_ACCESS_H
 #define ASM__RISCV__GUEST_ACCESS_H
 
+#include <xen/types.h>
+
+extern size_t _copy_to(uint64_t dest, const void *src, size_t len);
+extern size_t _copy_from(void *dest, uint64_t src, size_t len);
+
 unsigned long raw_copy_to_guest(void *to, const void *from, unsigned len);
 unsigned long raw_copy_from_guest(void *to, const void *from, unsigned len);
 unsigned long raw_clear_guest(void *to, unsigned int len);
-- 
2.43.0