[RFC PATCH v2 5/5] hvm: Allow specifying a prefered asid minimum

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 <[email protected]>
---
This is currently unused, but will prove useful for SEV-ES.

 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 b6df5cda35..65373b29f6 100644
--- a/xen/arch/x86/include/asm/hvm/asid.h
+++ b/xen/arch/x86/include/asm/hvm/asid.h
@@ -20,6 +20,7 @@ extern bool asid_enabled;
 #else
 #define asid_enabled (false)
 #endif
+extern unsigned long asid_default_min;
 
 /* Initialise ASID management distributed across all CPUs. */
 int hvm_asid_init(unsigned long nasids);
-- 
2.54.0



-- 
Teddy Astie | Vates XCP-ng Developer

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