[xen master] domain: map/unmap GADDR based shared guest areas

[patchbot@xxxxxxx]

commit eadc288cbb0ddc432ff8c9c639fb25b7538325de
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Oct 2 17:11:24 2023 +0200
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Thu Oct 5 14:10:45 2023 +0100

    domain: map/unmap GADDR based shared guest areas
    
    The registration by virtual/linear address has downsides: At least on
    x86 the access is expensive for HVM/PVH domains. Furthermore for 64-bit
    PV domains the areas are inaccessible (and hence cannot be updated by
    Xen) when in guest-user mode, and for HVM guests they may be
    inaccessible when Meltdown mitigations are in place. (There are yet
    more issues.)
    
    In preparation of the introduction of new vCPU operations allowing to
    register the respective areas (one of the two is x86-specific) by
    guest-physical address, flesh out the map/unmap functions.
    
    Noteworthy differences from map_vcpu_info():
    - areas can be registered more than once (and de-registered),
    - remote vCPU-s are paused rather than checked for being down (which in
      principle can change right after the check),
    - the domain lock is taken for a much smaller region.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
    Release-acked-by: Henry Wang <Henry.Wang@xxxxxxx>
---
 xen/common/domain.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 91 insertions(+), 1 deletion(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 47fc902719..747bf5c87a 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1605,7 +1605,82 @@ int map_guest_area(struct vcpu *v, paddr_t gaddr, 
unsigned int size,
                    struct guest_area *area,
                    void (*populate)(void *dst, struct vcpu *v))
 {
-    return -EOPNOTSUPP;
+    struct domain *d = v->domain;
+    void *map = NULL;
+    struct page_info *pg = NULL;
+    int rc = 0;
+
+    if ( ~gaddr ) /* Map (i.e. not just unmap)? */
+    {
+        unsigned long gfn = PFN_DOWN(gaddr);
+        unsigned int align;
+        p2m_type_t p2mt;
+
+        if ( gfn != PFN_DOWN(gaddr + size - 1) )
+            return -ENXIO;
+
+#ifdef CONFIG_COMPAT
+        if ( has_32bit_shinfo(d) )
+            align = alignof(compat_ulong_t);
+        else
+#endif
+            align = alignof(xen_ulong_t);
+        if ( !IS_ALIGNED(gaddr, align) )
+            return -ENXIO;
+
+        rc = check_get_page_from_gfn(d, _gfn(gfn), false, &p2mt, &pg);
+        if ( rc )
+            return rc;
+
+        if ( !get_page_type(pg, PGT_writable_page) )
+        {
+            put_page(pg);
+            return -EACCES;
+        }
+
+        map = __map_domain_page_global(pg);
+        if ( !map )
+        {
+            put_page_and_type(pg);
+            return -ENOMEM;
+        }
+        map += PAGE_OFFSET(gaddr);
+    }
+
+    if ( v != current )
+    {
+        if ( !spin_trylock(&d->hypercall_deadlock_mutex) )
+        {
+            rc = -ERESTART;
+            goto unmap;
+        }
+
+        vcpu_pause(v);
+
+        spin_unlock(&d->hypercall_deadlock_mutex);
+    }
+
+    domain_lock(d);
+
+    if ( map && populate )
+        populate(map, v);
+
+    SWAP(area->pg, pg);
+    SWAP(area->map, map);
+
+    domain_unlock(d);
+
+    if ( v != current )
+        vcpu_unpause(v);
+
+ unmap:
+    if ( pg )
+    {
+        unmap_domain_page_global(map);
+        put_page_and_type(pg);
+    }
+
+    return rc;
 }
 
 /*
@@ -1616,9 +1691,24 @@ int map_guest_area(struct vcpu *v, paddr_t gaddr, 
unsigned int size,
 void unmap_guest_area(struct vcpu *v, struct guest_area *area)
 {
     struct domain *d = v->domain;
+    void *map;
+    struct page_info *pg;
 
     if ( v != current )
         ASSERT(atomic_read(&v->pause_count) | atomic_read(&d->pause_count));
+
+    domain_lock(d);
+    map = area->map;
+    area->map = NULL;
+    pg = area->pg;
+    area->pg = NULL;
+    domain_unlock(d);
+
+    if ( pg )
+    {
+        unmap_domain_page_global(map);
+        put_page_and_type(pg);
+    }
 }
 
 int default_initialise_vcpu(struct vcpu *v, XEN_GUEST_HANDLE_PARAM(void) arg)
--
generated by git-patchbot for /home/xen/git/xen.git#master