[xen staging] xen/ioreq: Introduce domain_has_ioreq_server()

[patchbot@xxxxxxx]

commit 61eda016ca94d9dcacab10bd686374e2efc87416
Author:     Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
AuthorDate: Fri Jan 29 03:48:45 2021 +0200
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Fri Jan 29 16:55:23 2021 +0000

    xen/ioreq: Introduce domain_has_ioreq_server()
    
    This patch introduces a helper the main purpose of which is to check
    if a domain is using IOREQ server(s).
    
    On Arm the current benefit is to avoid calling 
vcpu_ioreq_handle_completion()
    (which implies iterating over all possible IOREQ servers anyway)
    on every return in leave_hypervisor_to_guest() if there is no active
    servers for the particular domain.
    Also this helper will be used by one of the subsequent patches on Arm.
    
    Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
    CC: Julien Grall <julien.grall@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
    [On Arm only]
    Tested-by: Wei Chen <Wei.Chen@xxxxxxx>
---
 xen/arch/arm/traps.c    | 15 +++++++++------
 xen/common/ioreq.c      | 16 ++++++++++++++++
 xen/include/xen/ioreq.h |  2 ++
 3 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index cb37a45b24..476900e6b8 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -2275,14 +2275,17 @@ static bool check_for_vcpu_work(void)
     struct vcpu *v = current;
 
 #ifdef CONFIG_IOREQ_SERVER
-    bool handled;
+    if ( domain_has_ioreq_server(v->domain) )
+    {
+        bool handled;
 
-    local_irq_enable();
-    handled = vcpu_ioreq_handle_completion(v);
-    local_irq_disable();
+        local_irq_enable();
+        handled = vcpu_ioreq_handle_completion(v);
+        local_irq_disable();
 
-    if ( !handled )
-        return true;
+        if ( !handled )
+            return true;
+    }
 #endif
 
     if ( likely(!v->arch.need_flush_to_ram) )
diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
index 07572a5c32..5b0f03e8b9 100644
--- a/xen/common/ioreq.c
+++ b/xen/common/ioreq.c
@@ -80,6 +80,22 @@ static ioreq_t *get_ioreq(struct ioreq_server *s, struct 
vcpu *v)
     return &p->vcpu_ioreq[v->vcpu_id];
 }
 
+/*
+ * This should only be used when d == current->domain or when they're
+ * distinct and d is paused. Otherwise the result is stale before
+ * the caller can inspect it.
+ */
+bool domain_has_ioreq_server(const struct domain *d)
+{
+    const struct ioreq_server *s;
+    unsigned int id;
+
+    FOR_EACH_IOREQ_SERVER(d, id, s)
+        return true;
+
+    return false;
+}
+
 static struct ioreq_vcpu *get_pending_vcpu(const struct vcpu *v,
                                            struct ioreq_server **srvp)
 {
diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
index 0b433e27ce..89ee171d92 100644
--- a/xen/include/xen/ioreq.h
+++ b/xen/include/xen/ioreq.h
@@ -83,6 +83,8 @@ static inline bool ioreq_needs_completion(const ioreq_t 
*ioreq)
 #define HANDLE_BUFIOREQ(s) \
     ((s)->bufioreq_handling != HVM_IOREQSRV_BUFIOREQ_OFF)
 
+bool domain_has_ioreq_server(const struct domain *d);
+
 bool vcpu_ioreq_pending(struct vcpu *v);
 bool vcpu_ioreq_handle_completion(struct vcpu *v);
 bool is_ioreq_server_page(struct domain *d, const struct page_info *page);
--
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