[Xen-devel] [PATCH v8 2/8] xen/arm: Add functions of mapping between vCPUID and virtual affinity

[Chen Baozi <cbz@xxxxxxxxxx>]

From: Chen Baozi <baozich@xxxxxxxxx>

GICv3 restricts that the maximum number of CPUs in affinity 0 (one
cluster) is 16. (See the note of 'Bits[15:0]' in '5.7.29 ICC_SGI0R_EL1
ICC_SGI1R_EL1 and ICC_ASGI1R_EL1, GICv3 Architecture Specification')
That is to say the upper 4 bits of affinity 0 is unused. Current
implementation considers that AFF0 is equal to vCPUID, which makes all
vCPUs in one cluster, limiting its number to 16. If we would like to
support more than 16 number of vCPU in one guest, we need to make use
of AFF1. Considering the unused upper 4 bits, we need to create a pair
of functions mapping the vCPUID and virtual affinity.

Signed-off-by: Chen Baozi <baozich@xxxxxxxxx>
Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>
---
 xen/include/asm-arm/domain.h | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index 75b17af..35b9a6d 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -266,6 +266,44 @@ static inline unsigned int domain_max_vcpus(const struct 
domain *d)
     return MAX_VIRT_CPUS;
 }
 
+/*
+ * Due to the restriction of GICv3, the number of vCPUs in AFF0 is
+ * limited to 16, thus only the first 4 bits of AFF0 are legal. We will
+ * use the first 2 affinity levels here, expanding the number of vCPU up
+ * to 4096 (16*256), which is more than the PEs that GIC-500 supports.
+ *
+ * Since we don't save information of vCPU's topology (affinity) in
+ * vMPIDR at the moment, we map the vcpuid to the vMPIDR linearly.
+ */
+static inline unsigned int vaffinity_to_vcpuid(register_t vaff)
+{
+    unsigned int vcpuid;
+
+    vaff &= MPIDR_HWID_MASK;
+
+    vcpuid = MPIDR_AFFINITY_LEVEL(vaff, 0);
+    vcpuid |= MPIDR_AFFINITY_LEVEL(vaff, 1) << 4;
+
+    return vcpuid;
+}
+
+static inline register_t vcpuid_to_vaffinity(unsigned int vcpuid)
+{
+    register_t vaff;
+
+    /*
+     * Right now only AFF0 and AFF1 are supported in virtual affinity.
+     * Since only the first 4 bits in AFF0 are used in GICv3, the
+     * available bits are 12 (4+8).
+     */
+    BUILD_BUG_ON(!(MAX_VIRT_CPUS < ((1 << 12))));
+
+    vaff = (vcpuid & 0x0f) << MPIDR_LEVEL_SHIFT(0);
+    vaff |= ((vcpuid >> 4) & MPIDR_LEVEL_MASK) << MPIDR_LEVEL_SHIFT(1);
+
+    return vaff;
+}
+
 #endif /* __ASM_DOMAIN_H__ */
 
 /*
-- 
2.1.4


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