[Xen-devel] [PATCH v2 1/3] xen/arm: io: Distinguish unhandled IO from aborted one

[Julien Grall <julien.grall@xxxxxxx>]

Currently, Xen is considering that an IO could either be handled or
unhandled. When unhandled, the stage-2 abort function will try another
way to resolve the abort.

However, the MMIO emulation may return unhandled when the address
belongs to an emulated range but was not correct. In that case, Xen
should avoid to try another way and directly inject a guest data abort.

Introduce a tri-state return to distinguish the following state:
    * IO_ABORT: The IO was handled but resulted in an abort
    * IO_HANDLED: The IO was handled
    * IO_UNHANDLED: The IO was unhandled

For now, it is considered that an IO belonging to an emulated range
could either be handled or inject an abort. This could be revisit in the
future if overlapped region exist (or we want to try another way to
resolve the abort).

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

---
    Changes in v2:
        - Always return IO_ABORT when the check failed because we know
        it was targeted emulated IO.
        - Fix typoes
---
 xen/arch/arm/io.c          | 32 ++++++++++++++++++--------------
 xen/arch/arm/traps.c       | 18 +++++++++++++++---
 xen/include/asm-arm/mmio.h | 13 ++++++++++---
 3 files changed, 43 insertions(+), 20 deletions(-)

diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c
index c3e9239ffe..1f4cb8f37d 100644
--- a/xen/arch/arm/io.c
+++ b/xen/arch/arm/io.c
@@ -26,8 +26,9 @@
 
 #include "decode.h"
 
-static int handle_read(const struct mmio_handler *handler, struct vcpu *v,
-                       mmio_info_t *info)
+static enum io_state handle_read(const struct mmio_handler *handler,
+                                 struct vcpu *v,
+                                 mmio_info_t *info)
 {
     const struct hsr_dabt dabt = info->dabt;
     struct cpu_user_regs *regs = guest_cpu_user_regs();
@@ -40,7 +41,7 @@ static int handle_read(const struct mmio_handler *handler, 
struct vcpu *v,
     uint8_t size = (1 << dabt.size) * 8;
 
     if ( !handler->ops->read(v, info, &r, handler->priv) )
-        return 0;
+        return IO_ABORT;
 
     /*
      * Sign extend if required.
@@ -60,17 +61,20 @@ static int handle_read(const struct mmio_handler *handler, 
struct vcpu *v,
 
     set_user_reg(regs, dabt.reg, r);
 
-    return 1;
+    return IO_HANDLED;
 }
 
-static int handle_write(const struct mmio_handler *handler, struct vcpu *v,
-                        mmio_info_t *info)
+static enum io_state handle_write(const struct mmio_handler *handler,
+                                  struct vcpu *v,
+                                  mmio_info_t *info)
 {
     const struct hsr_dabt dabt = info->dabt;
     struct cpu_user_regs *regs = guest_cpu_user_regs();
+    int ret;
 
-    return handler->ops->write(v, info, get_user_reg(regs, dabt.reg),
-                               handler->priv);
+    ret = handler->ops->write(v, info, get_user_reg(regs, dabt.reg),
+                              handler->priv);
+    return ( ret ) ? IO_HANDLED : IO_ABORT;
 }
 
 /* This function assumes that mmio regions are not overlapped */
@@ -103,9 +107,9 @@ static const struct mmio_handler *find_mmio_handler(struct 
domain *d,
     return handler;
 }
 
-int try_handle_mmio(struct cpu_user_regs *regs,
-                    const union hsr hsr,
-                    paddr_t gpa)
+enum io_state try_handle_mmio(struct cpu_user_regs *regs,
+                              const union hsr hsr,
+                              paddr_t gpa)
 {
     struct vcpu *v = current;
     const struct mmio_handler *handler = NULL;
@@ -119,11 +123,11 @@ int try_handle_mmio(struct cpu_user_regs *regs,
 
     handler = find_mmio_handler(v->domain, info.gpa);
     if ( !handler )
-        return 0;
+        return IO_UNHANDLED;
 
     /* All the instructions used on emulated MMIO region should be valid */
     if ( !dabt.valid )
-        return 0;
+        return IO_ABORT;
 
     /*
      * Erratum 766422: Thumb store translation fault to Hypervisor may
@@ -138,7 +142,7 @@ int try_handle_mmio(struct cpu_user_regs *regs,
         if ( rc )
         {
             gprintk(XENLOG_DEBUG, "Unable to decode instruction\n");
-            return 0;
+            return IO_ABORT;
         }
     }
 
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 2f8d790bb3..1e85f99ec1 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1964,10 +1964,21 @@ static void do_trap_stage2_abort_guest(struct 
cpu_user_regs *regs,
          *
          * Note that emulated region cannot be executed
          */
-        if ( is_data && try_handle_mmio(regs, hsr, gpa) )
+        if ( is_data )
         {
-            advance_pc(regs, hsr);
-            return;
+            enum io_state state = try_handle_mmio(regs, hsr, gpa);
+
+            switch ( state )
+            {
+            case IO_ABORT:
+                goto inject_abt;
+            case IO_HANDLED:
+                advance_pc(regs, hsr);
+                return;
+            case IO_UNHANDLED:
+                /* IO unhandled, try another way to handle it. */
+                break;
+            }
         }
 
         /*
@@ -1988,6 +1999,7 @@ static void do_trap_stage2_abort_guest(struct 
cpu_user_regs *regs,
                 hsr.bits, xabt.fsc);
     }
 
+inject_abt:
     gdprintk(XENLOG_DEBUG, "HSR=0x%x pc=%#"PRIregister" gva=%#"PRIvaddr
              " gpa=%#"PRIpaddr"\n", hsr.bits, regs->pc, gva, gpa);
     if ( is_data )
diff --git a/xen/include/asm-arm/mmio.h b/xen/include/asm-arm/mmio.h
index c941073257..c8dadb5006 100644
--- a/xen/include/asm-arm/mmio.h
+++ b/xen/include/asm-arm/mmio.h
@@ -32,6 +32,13 @@ typedef struct
     paddr_t gpa;
 } mmio_info_t;
 
+enum io_state
+{
+    IO_ABORT,       /* The IO was handled by the helper and led to an abort. */
+    IO_HANDLED,     /* The IO was successfully handled by the helper. */
+    IO_UNHANDLED,   /* The IO was not handled by the helper. */
+};
+
 typedef int (*mmio_read_t)(struct vcpu *v, mmio_info_t *info,
                            register_t *r, void *priv);
 typedef int (*mmio_write_t)(struct vcpu *v, mmio_info_t *info,
@@ -56,9 +63,9 @@ struct vmmio {
     struct mmio_handler *handlers;
 };
 
-int try_handle_mmio(struct cpu_user_regs *regs,
-                    const union hsr hsr,
-                    paddr_t gpa);
+enum io_state try_handle_mmio(struct cpu_user_regs *regs,
+                              const union hsr hsr,
+                              paddr_t gpa);
 void register_mmio_handler(struct domain *d,
                            const struct mmio_handler_ops *ops,
                            paddr_t addr, paddr_t size, void *priv);
-- 
2.11.0


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel