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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging] xen/riscv: add exception table support
commit a651dabf873d28692f1e4c2e57a3c47b560a16c4
Author: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
AuthorDate: Tue Mar 31 21:04:16 2026 +0200
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Apr 9 08:23:32 2026 +0200
xen/riscv: add exception table support
Introduce exception table handling for RISC-V so faults from selected
instructions can be recovered via fixup handlers instead of being
treated as fatal.
Add the RISC-V exception table format, sorting at boot to allow binary
search used furthuer, and lookup from the trap handler. Update the
linker script to emit the .ex_table section using introduced common
EX_TABLE macro shared with other architectures.
Also, reduce __start___ex_table alignment from 8 to 4 bytes to
match the natural alignment of struct exception_table_entry,
which contains two int32_t fields.
Add inclusion of asm/extable.h to asm/bug.h to deal with compilation
issue of common/virtual_region.c, which require declaration of
__start___ex_table and __stop___ex_table.
This implementation is based on Linux 6.16.
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
xen/arch/riscv/Kconfig | 1 +
xen/arch/riscv/Makefile | 1 +
xen/arch/riscv/extable.c | 84 ++++++++++++++++++++++++++++++++++++
xen/arch/riscv/include/asm/bug.h | 2 +
xen/arch/riscv/include/asm/extable.h | 58 +++++++++++++++++++++++++
xen/arch/riscv/setup.c | 3 ++
xen/arch/riscv/traps.c | 5 +++
xen/arch/riscv/xen.lds.S | 3 ++
xen/arch/x86/xen.lds.S | 6 +--
xen/include/xen/xen.lds.h | 6 +++
10 files changed, 164 insertions(+), 5 deletions(-)
diff --git a/xen/arch/riscv/Kconfig b/xen/arch/riscv/Kconfig
index 89876b3217..a5e87c1757 100644
--- a/xen/arch/riscv/Kconfig
+++ b/xen/arch/riscv/Kconfig
@@ -4,6 +4,7 @@ config RISCV
select GENERIC_BUG_FRAME
select GENERIC_UART_INIT
select HAS_DEVICE_TREE_DISCOVERY
+ select HAS_EX_TABLE
select HAS_PMAP
select HAS_UBSAN
select HAS_VMAP
diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
index ffbd7062e2..04f02ad89c 100644
--- a/xen/arch/riscv/Makefile
+++ b/xen/arch/riscv/Makefile
@@ -3,6 +3,7 @@ obj-y += cpufeature.o
obj-y += domain.o
obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
obj-y += entry.o
+obj-y += extable.o
obj-y += imsic.o
obj-y += intc.o
obj-y += irq.o
diff --git a/xen/arch/riscv/extable.c b/xen/arch/riscv/extable.c
new file mode 100644
index 0000000000..77e5e9e894
--- /dev/null
+++ b/xen/arch/riscv/extable.c
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <xen/init.h>
+#include <xen/bsearch.h>
+#include <xen/lib.h>
+#include <xen/livepatch.h>
+#include <xen/sort.h>
+#include <xen/virtual_region.h>
+
+#include <asm/extable.h>
+#include <asm/processor.h>
+
+#define EX_FIELD(ptr, field) ((unsigned long)&(ptr)->field + (ptr)->field)
+
+static inline unsigned long ex_insn(const struct exception_table_entry *ex)
+{
+ return EX_FIELD(ex, insn);
+}
+
+static inline unsigned long ex_fixup(const struct exception_table_entry *ex)
+{
+ return EX_FIELD(ex, fixup);
+}
+
+static void __init cf_check swap_ex(void *a, void *b)
+{
+ struct exception_table_entry *x = a, *y = b, tmp;
+ long delta = b - a;
+
+ tmp = *x;
+ x->insn = y->insn + delta;
+ y->insn = tmp.insn - delta;
+
+ x->fixup = y->fixup + delta;
+ y->fixup = tmp.fixup - delta;
+}
+
+static int cf_check cmp_ex(const void *a, const void *b)
+{
+ const unsigned long insn_a = ex_insn(a);
+ const unsigned long insn_b = ex_insn(b);
+
+ return (insn_a > insn_b) - (insn_a < insn_b);
+}
+
+void init_or_livepatch sort_exception_table(struct exception_table_entry
*start,
+ const struct exception_table_entry *stop)
+{
+ sort(start, stop - start, sizeof(*start), cmp_ex, swap_ex);
+}
+
+void __init sort_exception_tables(void)
+{
+ sort_exception_table(__start___ex_table, __stop___ex_table);
+}
+
+static void ex_handler_fixup(const struct exception_table_entry *ex,
+ struct cpu_user_regs *regs)
+{
+ regs->sepc = ex_fixup(ex);
+}
+
+bool fixup_exception(struct cpu_user_regs *regs)
+{
+ unsigned long pc = regs->sepc;
+ const struct virtual_region *region = find_text_region(pc);
+ const struct exception_table_entry *ex;
+ struct exception_table_entry key;
+
+ if ( !region || !region->ex )
+ return false;
+
+ key.insn = pc - (unsigned long)&key.insn;
+
+ ex = bsearch(&key, region->ex, region->ex_end - region->ex, sizeof(key),
+ cmp_ex);
+
+ if ( !ex )
+ return false;
+
+ ex_handler_fixup(ex, regs);
+
+ return true;
+}
diff --git a/xen/arch/riscv/include/asm/bug.h b/xen/arch/riscv/include/asm/bug.h
index 6ec8adc528..e6f2868816 100644
--- a/xen/arch/riscv/include/asm/bug.h
+++ b/xen/arch/riscv/include/asm/bug.h
@@ -9,6 +9,8 @@
#ifndef __ASSEMBLER__
+#include <asm/extable.h>
+
#define BUG_INSTR "unimp"
/*
diff --git a/xen/arch/riscv/include/asm/extable.h
b/xen/arch/riscv/include/asm/extable.h
new file mode 100644
index 0000000000..c0128a9181
--- /dev/null
+++ b/xen/arch/riscv/include/asm/extable.h
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef ASM__RISCV__ASM_EXTABLE_H
+#define ASM__RISCV__ASM_EXTABLE_H
+
+#ifdef __ASSEMBLER__
+
+#define ASM_EXTABLE(insn, fixup) \
+ .pushsection .ex_table, "a"; \
+ .balign 4; \
+ .word (insn) - .; \
+ .word (fixup) - .; \
+ .popsection
+
+.macro asm_extable, insn, fixup
+ ASM_EXTABLE(\insn, \fixup)
+.endm
+
+#else /* __ASSEMBLER__ */
+
+#include <xen/stringify.h>
+#include <xen/types.h>
+
+struct cpu_user_regs;
+
+#define ASM_EXTABLE(insn, fixup) \
+ ".pushsection .ex_table, \"a\"\n" \
+ ".balign 4\n" \
+ ".word (" #insn " - .)\n" \
+ ".word (" #fixup " - .)\n" \
+ ".popsection\n"
+
+/*
+ * The exception table consists of pairs of relative offsets: the first
+ * is the relative offset to an instruction that is allowed to fault,
+ * and the second is the relative offset at which the program should
+ * continue. No general-purpose registers are modified by the exception
+ * handling mechanism itself, so it is up to the fixup code to handle
+ * any necessary state cleanup.
+ *
+ * The exception table and fixup code live out of line with the main
+ * instruction path. This means when everything is well, we don't even
+ * have to jump over them. Further, they do not intrude on our cache or
+ * tlb entries.
+ */
+struct exception_table_entry {
+ int32_t insn, fixup;
+};
+
+extern struct exception_table_entry __start___ex_table[];
+extern struct exception_table_entry __stop___ex_table[];
+
+void sort_exception_tables(void);
+bool fixup_exception(struct cpu_user_regs *regs);
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* ASM__RISCV__ASM_EXTABLE_H */
diff --git a/xen/arch/riscv/setup.c b/xen/arch/riscv/setup.c
index cae49bb296..56a0907a85 100644
--- a/xen/arch/riscv/setup.c
+++ b/xen/arch/riscv/setup.c
@@ -19,6 +19,7 @@
#include <public/version.h>
+#include <asm/extable.h>
#include <asm/cpufeature.h>
#include <asm/early_printk.h>
#include <asm/fixmap.h>
@@ -81,6 +82,8 @@ void __init noreturn start_xen(unsigned long bootcpu_id,
smp_prepare_boot_cpu();
+ sort_exception_tables();
+
set_cpuid_to_hartid(0, bootcpu_id);
trap_init();
diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c
index 326f2be628..d35c013e13 100644
--- a/xen/arch/riscv/traps.c
+++ b/xen/arch/riscv/traps.c
@@ -12,6 +12,7 @@
#include <xen/sched.h>
#include <xen/softirq.h>
+#include <asm/extable.h>
#include <asm/cpufeature.h>
#include <asm/intc.h>
#include <asm/processor.h>
@@ -217,6 +218,10 @@ void do_trap(struct cpu_user_regs *cpu_regs)
break;
}
+
+ if ( fixup_exception(cpu_regs) )
+ break;
+
fallthrough;
default:
if ( cause & CAUSE_IRQ_FLAG )
diff --git a/xen/arch/riscv/xen.lds.S b/xen/arch/riscv/xen.lds.S
index 331a7d63d3..65f136dce9 100644
--- a/xen/arch/riscv/xen.lds.S
+++ b/xen/arch/riscv/xen.lds.S
@@ -74,6 +74,9 @@ SECTIONS
.data.ro_after_init : {
__ro_after_init_start = .;
*(.data.ro_after_init)
+
+ EX_TABLE
+
. = ALIGN(PAGE_SIZE);
__ro_after_init_end = .;
} : text
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index c326538ebb..b9e888e596 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -113,11 +113,7 @@ SECTIONS
__ro_after_init_start = .;
*(.data.ro_after_init)
- . = ALIGN(8);
- /* Exception table */
- __start___ex_table = .;
- *(.ex_table)
- __stop___ex_table = .;
+ EX_TABLE
. = ALIGN(PAGE_SIZE);
__ro_after_init_end = .;
diff --git a/xen/include/xen/xen.lds.h b/xen/include/xen/xen.lds.h
index 136849ecd5..ea11e3fb62 100644
--- a/xen/include/xen/xen.lds.h
+++ b/xen/include/xen/xen.lds.h
@@ -219,4 +219,10 @@
#define VPCI_ARRAY
#endif
+#define EX_TABLE \
+ . = ALIGN(4); \
+ __start___ex_table = .; \
+ *(.ex_table) \
+ __stop___ex_table = .;
+
#endif /* __XEN_LDS_H__ */
--
generated by git-patchbot for /home/xen/git/xen.git#staging
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