[Xen-devel] [PATCH v4 15/27] ARM: vITS: introduce translation table walks

[Andre Przywara <andre.przywara@xxxxxxx>]

The ITS stores the target (v)CPU and the (virtual) LPI number in tables.
Introduce functions to walk those tables and translate an device ID -
event ID pair into a pair of virtual LPI and vCPU.
We map those tables on demand - which is cheap on arm64. Also we take
care of the locking on the way, since we can't easily protect those ITTs
from being altered by the guest.

To allow compiling without warnings, we declare two functions as
non-static for the moment, which two later patches will fix.

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
---
 xen/arch/arm/vgic-v3-its.c | 183 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 183 insertions(+)

diff --git a/xen/arch/arm/vgic-v3-its.c b/xen/arch/arm/vgic-v3-its.c
index fd3b9a1..fcfea3b 100644
--- a/xen/arch/arm/vgic-v3-its.c
+++ b/xen/arch/arm/vgic-v3-its.c
@@ -71,6 +71,189 @@ static bool its_is_enabled(struct virt_its *its)
     return test_bit(VIRT_ITS_ENABLED, &its->flags);
 }
 
+#define UNMAPPED_COLLECTION      ((uint16_t)~0)
+
+/*
+ * The physical address is encoded slightly differently depending on
+ * the used page size: the highest four bits are stored in the lowest
+ * four bits of the field for 64K pages.
+ */
+static paddr_t get_baser_phys_addr(uint64_t reg)
+{
+    if ( reg & BIT(9) )
+        return (reg & GENMASK_ULL(47, 16)) |
+                ((reg & GENMASK_ULL(15, 12)) << 36);
+    else
+        return reg & GENMASK_ULL(47, 12);
+}
+
+/* Must be called with the ITS lock held. */
+static struct vcpu *get_vcpu_from_collection(struct virt_its *its,
+                                             uint16_t collid)
+{
+    paddr_t addr = get_baser_phys_addr(its->baser_coll);
+    uint16_t *coll_table;
+    uint16_t vcpu_id;
+
+    if ( collid >= its->max_collections )
+        return NULL;
+
+    coll_table = map_one_guest_page(its->d, addr + collid * sizeof(uint16_t));
+    if ( !coll_table )
+        return NULL;
+
+    vcpu_id = *coll_table;
+
+    unmap_one_guest_page(coll_table);
+
+    if ( vcpu_id == UNMAPPED_COLLECTION || vcpu_id >= its->d->max_vcpus )
+        return NULL;
+
+    return its->d->vcpu[vcpu_id];
+}
+
+/*
+ * Our device table encodings:
+ * Contains the guest physical address of the Interrupt Translation Table in
+ * bits [51:8], and the size of it encoded in the lowest 8 bits.
+ */
+#define DEV_TABLE_ITT_ADDR(x) ((x) & GENMASK_ULL(51, 8))
+#define DEV_TABLE_ITT_SIZE(x) (BIT(((x) & GENMASK_ULL(7, 0)) + 1))
+#define DEV_TABLE_ENTRY(addr, bits)                     \
+        (((addr) & GENMASK_ULL(51, 8)) | (((bits) - 1) & GENMASK_ULL(7, 0)))
+
+/*
+ * Lookup the address of the Interrupt Translation Table associated with
+ * a device ID and return the address of the ITTE belonging to the event ID
+ * (which is an index into that table).
+ */
+static paddr_t its_get_itte_address(struct virt_its *its,
+                                    uint32_t devid, uint32_t evid)
+{
+    paddr_t ret, addr = get_baser_phys_addr(its->baser_dev);
+    uint64_t *itt_ptr;
+    uint64_t itt;
+
+    if ( devid >= its->max_devices )
+        return INVALID_PADDR;
+
+    itt_ptr = map_one_guest_page(its->d, addr + devid * sizeof(uint64_t));
+    if ( !itt_ptr )
+        return INVALID_PADDR;
+
+    itt = read_u64_atomic(itt_ptr);
+
+    if ( evid < DEV_TABLE_ITT_SIZE(itt) &&
+         DEV_TABLE_ITT_ADDR(itt) != INVALID_PADDR )
+        ret = DEV_TABLE_ITT_ADDR(itt) + evid * sizeof(struct vits_itte);
+    else
+        ret = INVALID_PADDR;
+
+    unmap_one_guest_page(itt_ptr);
+
+    return ret;
+}
+
+/*
+ * Looks up a given deviceID/eventID pair on an ITS and returns a pointer to
+ * the corresponding ITTE. This maps the respective guest page into Xen.
+ * Once finished with handling the ITTE, call put_itte() to unmap
+ * the page again.
+ * Must be called with the ITS lock held.
+ */
+static struct vits_itte *get_itte(struct virt_its *its,
+                                  uint32_t devid, uint32_t evid)
+{
+    paddr_t addr = its_get_itte_address(its, devid, evid);
+
+    if ( addr == INVALID_PADDR )
+        return NULL;
+
+    return map_one_guest_page(its->d, addr);
+}
+
+/* Must be called with the ITS lock held. */
+static void put_itte(struct virt_its *its, struct vits_itte *itte)
+{
+    unmap_one_guest_page(itte);
+}
+
+/*
+ * Queries the collection and device tables to get the vCPU and virtual
+ * LPI number for a given guest event. This takes care of mapping the
+ * respective tables and validating the values, since we can't efficiently
+ * protect the ITTs with their less-than-page-size granularity.
+ * This function takes care of the locking by taking the its_lock itself, so
+ * a caller shall not hold this. Upon returning, the lock is dropped again.
+ */
+bool read_itte(struct virt_its *its, uint32_t devid, uint32_t evid,
+               struct vcpu **vcpu, uint32_t *vlpi)
+{
+    struct vits_itte *itte;
+    uint16_t collid;
+    uint32_t _vlpi;
+    struct vcpu *_vcpu;
+
+    spin_lock(&its->its_lock);
+    itte = get_itte(its, devid, evid);
+    if ( !itte )
+    {
+        spin_unlock(&its->its_lock);
+        return false;
+    }
+    collid = itte->collection;
+    _vlpi = itte->vlpi;
+    put_itte(its, itte);
+
+    _vcpu = get_vcpu_from_collection(its, collid);
+    spin_unlock(&its->its_lock);
+
+    if ( !_vcpu )
+        return false;
+
+    *vcpu = _vcpu;
+    *vlpi = _vlpi;
+
+    return true;
+}
+
+#define SKIP_LPI_UPDATE 1
+/*
+ * This function takes care of the locking by taking the its_lock itself, so
+ * a caller shall not hold this. Upon returning, the lock is dropped again.
+ */
+bool write_itte(struct virt_its *its, uint32_t devid, uint32_t evid,
+                uint32_t collid, uint32_t vlpi, struct vcpu **vcpu)
+{
+    struct vits_itte *itte;
+
+    if ( collid >= its->max_collections )
+        return false;
+
+    if ( vlpi >= its->d->arch.vgic.nr_lpis )
+        return false;
+
+    spin_lock(&its->its_lock);
+    itte = get_itte(its, devid, evid);
+    if ( !itte )
+    {
+        spin_unlock(&its->its_lock);
+        return false;
+    }
+
+    itte->collection = collid;
+    if ( vlpi != SKIP_LPI_UPDATE )
+        itte->vlpi = vlpi;
+
+    if ( vcpu )
+        *vcpu = get_vcpu_from_collection(its, collid);
+
+    put_itte(its, itte);
+    spin_unlock(&its->its_lock);
+
+    return true;
+}
+
 /**************************************
  * Functions that handle ITS commands *
  **************************************/
-- 
2.9.0


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