[Xen-devel] [PATCH v3 22/38] arm/p2m: Make get_page_from_gva ready for altp2m

[Sergej Proskurin <proskurin@xxxxxxxxxxxxx>]

The function get_page_from_gva uses ARM's hardware support to translate
gva's to machine addresses. This function is used, among others, for
memory regulation purposes, e.g, within the context of memory ballooning.
To ensure correct behavior while altp2m is in use, we use the host's p2m
table for the associated gva to ma translation. This is required at this
point, as altp2m lazily copies pages from the host's p2m and even might
be flushed because of changes to the host's p2m (as it is done within
the context of memory ballooning).

Signed-off-by: Sergej Proskurin <proskurin@xxxxxxxxxxxxx>
---
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
---
v3: Cosmetic fixes.

    Make use of the p2m_(switch|restore)_vttbr_and_(g|s)et_flags macros
    to avoid code duplication.
---
 xen/arch/arm/p2m.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 15abd39..06f7eb8 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1581,7 +1581,24 @@ struct page_info *get_page_from_gva(struct vcpu *v, 
vaddr_t va,
 
     p2m_read_lock(p2m);
 
-    rc = gvirt_to_maddr(va, &maddr, flags);
+    /*
+     * If altp2m is active, we need to translate the gva upon the hostp2m's
+     * vttbr, as it contains all valid mappings while the currently active
+     * altp2m view might not have the required gva mapping yet.
+     */
+    if ( unlikely(altp2m_active(d)) )
+    {
+        unsigned long flags = 0;
+        uint64_t ovttbr = READ_SYSREG64(VTTBR_EL2);
+
+        p2m_switch_vttbr_and_get_flags(ovttbr, p2m->vttbr, flags);
+
+        rc = gvirt_to_maddr(va, &maddr, flags);
+
+        p2m_restore_vttbr_and_set_flags(ovttbr, flags);
+    }
+    else
+        rc = gvirt_to_maddr(va, &maddr, flags);
 
     if ( rc )
         goto err;
-- 
2.9.0


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