[RFC PATCH 7/7] hvm: Allow specifying a prefered asid minimum

["Teddy Astie" <teddy.astie@xxxxxxxxxx>]

To avoid clobbering all ASIDs that are below SEV-enabled guest maximum,
we want to allocate if possible all ASID over a "prefered minimum"
and fallback to below otherwise.

Signed-off-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
---
 xen/arch/x86/hvm/asid.c             | 8 ++++++++
 xen/arch/x86/include/asm/hvm/asid.h | 1 +
 2 files changed, 9 insertions(+)

diff --git a/xen/arch/x86/hvm/asid.c b/xen/arch/x86/hvm/asid.c
index 1a21125161..4ad3200c96 100644
--- a/xen/arch/x86/hvm/asid.c
+++ b/xen/arch/x86/hvm/asid.c
@@ -22,6 +22,9 @@ boolean_param("asid", opt_asid_enabled);
 bool __read_mostly asid_enabled = false;
 static unsigned long __ro_after_init *asid_bitmap;
 static unsigned long __ro_after_init asid_count;
+
+/* Default minimum ASID to use */
+unsigned long __read_mostly asid_default_min = 0;
 static DEFINE_SPINLOCK(asid_lock);
 
 /*
@@ -67,6 +70,11 @@ int hvm_asid_alloc(struct hvm_asid *asid)
         return 0;
     }
 
+    /* Try to allocate above default minimum */
+    if ( asid_default_min &&
+         !hvm_asid_alloc_range(asid, asid_default_min, asid_count) )
+        return 0;
+
     spin_lock(&asid_lock);
     new_asid = find_first_zero_bit(asid_bitmap, asid_count);
     if ( new_asid > asid_count )
diff --git a/xen/arch/x86/include/asm/hvm/asid.h 
b/xen/arch/x86/include/asm/hvm/asid.h
index 13ea357f70..e989ebbe8c 100644
--- a/xen/arch/x86/include/asm/hvm/asid.h
+++ b/xen/arch/x86/include/asm/hvm/asid.h
@@ -16,6 +16,7 @@ struct hvm_asid {
 };
 
 extern bool asid_enabled;
+extern unsigned long asid_default_min;
 
 /* Initialise ASID management distributed across all CPUs. */
 int hvm_asid_init(unsigned long nasids);
-- 
2.52.0



--
Teddy Astie | Vates XCP-ng Developer

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