[PATCH V2 21/23] xen/arm: Add mapcache invalidation handling

[Oleksandr Tyshchenko <olekstysh@gmail.com>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

We need to send mapcache invalidation request to qemu/demu everytime
the page gets removed from a guest.

At the moment, the Arm code doesn't explicitely remove the existing
mapping before inserting the new mapping. Instead, this is done
implicitely by __p2m_set_entry().

So the corresponding flag will be set in __p2m_set_entry() if old entry
is a RAM page *and* the new MFN is different. And the invalidation
request will be sent in do_trap_hypercall() later on.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
CC: Julien Grall <julien.grall@arm.com>

---
Please note, this is a split/cleanup/hardening of Julien's PoC:
"Add support for Guest IO forwarding to a device emulator"

Changes V1 -> V2:
   - new patch, some changes were derived from (+ new explanation):
     xen/ioreq: Make x86's invalidate qemu mapcache handling common
   - put setting of the flag into __p2m_set_entry()
   - clarify the conditions when the flag should be set
   - use domain_has_ioreq_server()
   - update do_trap_hypercall() by adding local variable
---
 xen/arch/arm/p2m.c   |  8 ++++++++
 xen/arch/arm/traps.c | 13 ++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 370173c..2693b0c 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1,6 +1,7 @@
 #include <xen/cpu.h>
 #include <xen/domain_page.h>
 #include <xen/iocap.h>
+#include <xen/ioreq.h>
 #include <xen/lib.h>
 #include <xen/sched.h>
 #include <xen/softirq.h>
@@ -1067,7 +1068,14 @@ static int __p2m_set_entry(struct p2m_domain *p2m,
      */
     if ( p2m_is_valid(orig_pte) &&
          !mfn_eq(lpae_get_mfn(*entry), lpae_get_mfn(orig_pte)) )
+    {
+#ifdef CONFIG_IOREQ_SERVER
+        if ( domain_has_ioreq_server(p2m->domain) &&
+             (p2m->domain == current->domain) && p2m_is_ram(orig_pte.p2m.type) )
+            p2m->domain->qemu_mapcache_invalidate = true;
+#endif
         p2m_free_entry(p2m, orig_pte, level);
+    }
 
 out:
     unmap_domain_page(table);
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index a8f5fdf..9eaa342 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1442,6 +1442,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr,
                               const union hsr hsr)
 {
     arm_hypercall_fn_t call = NULL;
+    struct vcpu *v = current;
 
     BUILD_BUG_ON(NR_hypercalls < ARRAY_SIZE(arm_hypercall_table) );
 
@@ -1458,7 +1459,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr,
         return;
     }
 
-    current->hcall_preempted = false;
+    v->hcall_preempted = false;
 
     perfc_incra(hypercalls, *nr);
     call = arm_hypercall_table[*nr].fn;
@@ -1471,7 +1472,7 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr,
     HYPERCALL_RESULT_REG(regs) = call(HYPERCALL_ARGS(regs));
 
 #ifndef NDEBUG
-    if ( !current->hcall_preempted )
+    if ( !v->hcall_preempted )
     {
         /* Deliberately corrupt parameter regs used by this hypercall. */
         switch ( arm_hypercall_table[*nr].nr_args ) {
@@ -1488,8 +1489,14 @@ static void do_trap_hypercall(struct cpu_user_regs *regs, register_t *nr,
 #endif
 
     /* Ensure the hypercall trap instruction is re-executed. */
-    if ( current->hcall_preempted )
+    if ( v->hcall_preempted )
         regs->pc -= 4;  /* re-execute 'hvc #XEN_HYPERCALL_TAG' */
+
+#ifdef CONFIG_IOREQ_SERVER
+    if ( unlikely(v->domain->qemu_mapcache_invalidate) &&
+         test_and_clear_bool(v->domain->qemu_mapcache_invalidate) )
+        send_invalidate_ioreq();
+#endif
 }
 
 void arch_hypercall_tasklet_result(struct vcpu *v, long res)
-- 
2.7.4