xen/arm: p2m: Perform local TLB invalidation on vCPU migration

The ARM architecture allows an OS to have per-CPU page tables, as it
guarantees that TLBs never migrate from one CPU to another.

This works fine until this is done in a guest. Consider the following
scenario:
    - vcpu-0 maps P to V
    - vpcu-1 maps P' to V

If run on the same physical CPU, vcpu-1 can hit in TLBs generated by
vcpu-0 accesses, and access the wrong physical page.

The solution to this is to keep a per-p2m map of which vCPU ran the last
on each given pCPU and invalidate local TLBs if two vPCUs from the same
VM run on the same CPU.

Unfortunately it is not possible to allocate per-cpu variable on the
fly. So for now the size of the array is NR_CPUS, this is fine because
we still have space in the structure domain. We may want to add an
helper to allocate per-cpu variable in the future.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 1fc6ca3bb2e7562c6bfc78f6096ddb22ea16cef8..626376090d6b92701bb8a39b6f42c6ece5d323d6 100644 (file)
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -130,6 +130,7 @@ void p2m_restore_state(struct vcpu *n)
 {
     register_t hcr;
     struct p2m_domain *p2m = &n->domain->arch.p2m;
+    uint8_t *last_vcpu_ran;
 
     if ( is_idle_vcpu(n) )
         return;
@@ -149,6 +150,17 @@ void p2m_restore_state(struct vcpu *n)
 
     WRITE_SYSREG(hcr, HCR_EL2);
     isb();
+
+    last_vcpu_ran = &p2m->last_vcpu_ran[smp_processor_id()];
+
+    /*
+     * Flush local TLB for the domain to prevent wrong TLB translation
+     * when running multiple vCPU of the same domain on a single pCPU.
+     */
+    if ( *last_vcpu_ran != INVALID_VCPU_ID && *last_vcpu_ran != n->vcpu_id )
+        flush_tlb_local();
+
+    *last_vcpu_ran = n->vcpu_id;
 }
 
 static void p2m_flush_tlb(struct p2m_domain *p2m)
@@ -1247,6 +1259,7 @@ int p2m_init(struct domain *d)
 {
     struct p2m_domain *p2m = &d->arch.p2m;
     int rc = 0;
+    unsigned int cpu;
 
     rwlock_init(&p2m->lock);
     INIT_PAGE_LIST_HEAD(&p2m->pages);
@@ -1275,6 +1288,17 @@ int p2m_init(struct domain *d)
 
     rc = p2m_alloc_table(d);
 
+    /*
+     * Make sure that the type chosen to is able to store the an vCPU ID
+     * between 0 and the maximum of virtual CPUS supported as long as
+     * the INVALID_VCPU_ID.
+     */
+    BUILD_BUG_ON((1 << (sizeof(p2m->last_vcpu_ran[0]) * 8)) < MAX_VIRT_CPUS);
+    BUILD_BUG_ON((1 << (sizeof(p2m->last_vcpu_ran[0])* 8)) < INVALID_VCPU_ID);
+
+    for_each_possible_cpu(cpu)
+       p2m->last_vcpu_ran[cpu] = INVALID_VCPU_ID;
+
     return rc;
 }
 

diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index 089952308479ae01bce89cc8d9b683a2b41d6137..18c57f936e81d6bd74c290eec1b6c1f27ef96537 100644 (file)
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -96,6 +96,9 @@ struct p2m_domain {
 
     /* back pointer to domain */
     struct domain *domain;
+
+    /* Keeping track on which CPU this p2m was used and for which vCPU */
+    uint8_t last_vcpu_ran[NR_CPUS];
 };
 
 /*