[Xen-devel] [PATCH 3/4] xen/arm: set vpidr on the pcpu where the vcpu will run

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On big.LITTLE systems not all cores have the same midr. Instead of
initializing the vpidr to the boot cpu midr, set it to the value of the
midr of the pcpu where the vcpu will run.

This way, assuming that the vcpu has been created with the right pcpu
affinity, the guest will be able to read the right vpidr value, matching
the one of the physical cpu.

Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/domain.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 532e824..280125f 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -315,6 +315,22 @@ static void schedule_tail(struct vcpu *prev)
 static void continue_new_vcpu(struct vcpu *prev)
 {
     current->arch.actlr = READ_SYSREG32(ACTLR_EL1);
+    /*
+     * Default the virtual ID to match the physical.
+     *
+     * In case the big.LITTLE systems, a guest should be created with
+     * cpu affinity set so that all vcpus run on the same kind of pcpus.
+     * Warn if it is not the case.
+     */
+    if ( !current->domain->arch.vpidr )
+        current->domain->arch.vpidr = current_cpu_data.midr.bits;
+    else if ( current->domain->arch.vpidr != current_cpu_data.midr.bits )
+    {
+        gdprintk(XENLOG_WARNING,
+                 "WARNING: possible corruptions! d%uv%u is running on a pcpu 
with different midr (%x) from the others (%x)\n",
+                 current->domain->domain_id, current->vcpu_id,
+                 current_cpu_data.midr.bits, current->domain->arch.vpidr);
+    }
 
     schedule_tail(prev);
 
@@ -596,9 +612,6 @@ int arch_domain_create(struct domain *d, unsigned int 
domcr_flags,
     if ( (d->shared_info = alloc_xenheap_pages(0, 0)) == NULL )
         goto fail;
 
-    /* Default the virtual ID to match the physical */
-    d->arch.vpidr = boot_cpu_data.midr.bits;
-
     clear_page(d->shared_info);
     share_xen_page_with_guest(
         virt_to_page(d->shared_info), d, XENSHARE_writable);
-- 
1.9.1


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