[PATCH 2/2] xen/arm: Support runstate crossing pages

[Bertrand Marquis <bertrand.marquis@xxxxxxx>]

Add support for runstate area register with the structure crossing pages
The code is storing up to 2 pages reference during the hypercall.
During a context switch, the code is computing where the
state_entry_time is and is breaking the memcpy in 2 parts when it is
required.

Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
---
 xen/arch/arm/domain.c        | 101 +++++++++++++++++++++++++----------
 xen/include/asm-arm/domain.h |   5 +-
 2 files changed, 76 insertions(+), 30 deletions(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 739059234f..d847cb00f2 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -280,11 +280,16 @@ void arch_cleanup_runstate_guest(struct vcpu *v)
 {
     spin_lock(&v->arch.runstate_guest.lock);
 
-    /* cleanup previous page if any */
-    if ( v->arch.runstate_guest.page )
+    /* cleanup previous pages if any */
+    if ( v->arch.runstate_guest.page[0] )
     {
-        put_page_and_type(v->arch.runstate_guest.page);
-        v->arch.runstate_guest.page = NULL;
+        put_page_and_type(v->arch.runstate_guest.page[0]);
+        v->arch.runstate_guest.page[0] = NULL;
+        if ( v->arch.runstate_guest.page[1] )
+        {
+            put_page_and_type(v->arch.runstate_guest.page[1]);
+            v->arch.runstate_guest.page[1] = NULL;
+        }
         v->arch.runstate_guest.offset = 0;
     }
 
@@ -294,26 +299,25 @@ void arch_cleanup_runstate_guest(struct vcpu *v)
 int arch_setup_runstate_guest(struct vcpu *v,
                             struct vcpu_register_runstate_memory_area area)
 {
-    struct page_info *page;
+    struct page_info *page[2] = {NULL,NULL};
     unsigned offset;
 
     spin_lock(&v->arch.runstate_guest.lock);
 
-    /* cleanup previous page if any */
-    if ( v->arch.runstate_guest.page )
+    /* cleanup previous pages if any */
+    if ( v->arch.runstate_guest.page[0] )
     {
-        put_page_and_type(v->arch.runstate_guest.page);
-        v->arch.runstate_guest.page = NULL;
+        put_page_and_type(v->arch.runstate_guest.page[0]);
+        v->arch.runstate_guest.page[0] = NULL;
+        if ( v->arch.runstate_guest.page[1] )
+        {
+            put_page_and_type(v->arch.runstate_guest.page[1]);
+            v->arch.runstate_guest.page[1] = NULL;
+        }
         v->arch.runstate_guest.offset = 0;
     }
 
     offset = ((vaddr_t)area.addr.v) & ~PAGE_MASK;
-    if ( offset > (PAGE_SIZE - sizeof(struct vcpu_runstate_info)) )
-    {
-        spin_unlock(&v->arch.runstate_guest.lock);
-        gprintk(XENLOG_DEBUG, "Runstate is crossing pages\n");
-        return -EINVAL;
-    }
 
     /* provided address must be aligned to a 64bit */
     if ( offset % alignof(struct vcpu_runstate_info) )
@@ -323,15 +327,30 @@ int arch_setup_runstate_guest(struct vcpu *v,
         return -EINVAL;
     }
 
-    page = get_page_from_gva(v, (vaddr_t)area.addr.v, GV2M_WRITE);
-    if ( !page )
+    page[0] = get_page_from_gva(v, (vaddr_t)area.addr.v, GV2M_WRITE);
+    if ( !page[0] )
     {
         spin_unlock(&v->arch.runstate_guest.lock);
         gprintk(XENLOG_DEBUG, "Runstate pointer is not mapped\n");
         return -EINVAL;
     }
 
-    v->arch.runstate_guest.page = page;
+    if ( offset > (PAGE_SIZE - sizeof(struct vcpu_runstate_info)) )
+    {
+        /* guest area is crossing pages */
+        page[1] = get_page_from_gva(v, (vaddr_t)area.addr.v + PAGE_SIZE,
+                                        GV2M_WRITE);
+        if ( !page[1] )
+        {
+            put_page_and_type(v->arch.runstate_guest.page[0]);
+            spin_unlock(&v->arch.runstate_guest.lock);
+            gprintk(XENLOG_DEBUG, "Runstate pointer is not fully mapped\n");
+            return -EINVAL;
+        }
+    }
+
+    v->arch.runstate_guest.page[0] = page[0];
+    v->arch.runstate_guest.page[1] = page[1];
     v->arch.runstate_guest.offset = offset;
 
     spin_unlock(&v->arch.runstate_guest.lock);
@@ -343,34 +362,60 @@ int arch_setup_runstate_guest(struct vcpu *v,
 /* Update per-VCPU guest runstate shared memory area (if registered). */
 static void update_runstate_area(struct vcpu *v)
 {
-    struct vcpu_runstate_info *guest_runstate;
-    void *p;
+    void *p[2];
+    unsigned offset, time_offset;
+    uint64_t *state_entry_time;
 
     spin_lock(&v->arch.runstate_guest.lock);
 
-    if ( v->arch.runstate_guest.page )
+    if ( v->arch.runstate_guest.page[0] )
     {
-        p = __map_domain_page(v->arch.runstate_guest.page);
-        guest_runstate = p + v->arch.runstate_guest.offset;
+        p[0] = __map_domain_page(v->arch.runstate_guest.page[0]);
+        if ( v->arch.runstate_guest.page[1] )
+            p[1] = __map_domain_page(v->arch.runstate_guest.page[1]);
+        else
+            p[1] = NULL;
+        offset = v->arch.runstate_guest.offset;
 
         if ( VM_ASSIST(v->domain, runstate_update_flag) )
         {
+            time_offset = offset +
+                    offsetof(struct vcpu_runstate_info, state_entry_time);
+
+            if ( time_offset < PAGE_SIZE )
+                state_entry_time = p[0] + time_offset;
+            else
+                state_entry_time = p[1] + (time_offset - PAGE_SIZE);
+
             v->runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
-            guest_runstate->state_entry_time |= XEN_RUNSTATE_UPDATE;
+            *state_entry_time |= XEN_RUNSTATE_UPDATE;
             smp_wmb();
         }
+        else
+            state_entry_time = NULL;
+
+        if ( p[1] )
+        {
+            memcpy(p[0] + offset, &v->runstate, PAGE_SIZE - offset);
+            memcpy(p[1], &v->runstate + (PAGE_SIZE - offset),
+                    sizeof(v->runstate) - (PAGE_SIZE - offset));
+        }
+        else
+            memcpy(p[0] + offset, &v->runstate, sizeof(v->runstate));
 
-        memcpy(guest_runstate, &v->runstate, sizeof(v->runstate));
+        /* copy must be done before switching the bit */
         smp_wmb();
 
-        if ( VM_ASSIST(v->domain, runstate_update_flag) )
+        if ( state_entry_time )
         {
             v->runstate.state_entry_time &= ~XEN_RUNSTATE_UPDATE;
-            guest_runstate->state_entry_time &= ~XEN_RUNSTATE_UPDATE;
+            *state_entry_time &= ~XEN_RUNSTATE_UPDATE;
             smp_wmb();
         }
 
-        unmap_domain_page(p);
+        unmap_domain_page(p[0]);
+        if ( p[1] )
+            unmap_domain_page(p[1]);
     }
 
     spin_unlock(&v->arch.runstate_guest.lock);
diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index 3a7f53e13d..61e32f1ed5 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -209,8 +209,9 @@ struct arch_vcpu
 
     /* runstate guest info */
     struct {
-        struct page_info *page;  /* guest page */
-        unsigned         offset; /* offset in page */
+        /* we need 2 pages in case the guest area is crossing pages */
+        struct page_info *page[2];  /* guest pages */
+        unsigned         offset; /* offset in first page */
         spinlock_t       lock;   /* lock to access page */
     } runstate_guest;
 
-- 
2.17.1