[Xen-devel] [PATCH 18/22] xen/arm: p2m: Rework the context switch to another VTTBR in flush_tlb_domain

[Julien Grall <julien.grall@xxxxxxx>]

The current implementation of flush_tlb_domain is relying on the domain
to have a single p2m. With the upcoming feature altp2m, a single domain
may have different p2m. So we would need to switch to the correct p2m in
order to flush the TLBs.

Rather than checking whether the domain is not the current domain, check
whether the VTTBR is different. The resulting assembly code is much
smaller: from 38 instructions (+ 2 functions call) to 22 instructions.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/arm/p2m.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index d1b6009..015c1e8 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -151,24 +151,28 @@ void p2m_restore_state(struct vcpu *n)
 
 void flush_tlb_domain(struct domain *d)
 {
+    struct p2m_domain *p2m = &d->arch.p2m;
     unsigned long flags = 0;
+    uint64_t ovttbr;
 
     /*
-     * Update the VTTBR if necessary with the domain d. In this case,
-     * it's only necessary to flush TLBs on every CPUs with the current VMID
-     * (our domain).
+     * ARM only provides an instruction to flush TLBs for the current
+     * VMID. So switch to the VTTBR of a given P2M if different.
      */
-    if ( d != current->domain )
+    ovttbr = READ_SYSREG64(VTTBR_EL2);
+    if ( ovttbr != p2m->vttbr )
     {
         local_irq_save(flags);
-        p2m_load_VTTBR(d);
+        WRITE_SYSREG64(p2m->vttbr, VTTBR_EL2);
+        isb();
     }
 
     flush_tlb();
 
-    if ( d != current->domain )
+    if ( ovttbr != READ_SYSREG64(VTTBR_EL2) )
     {
-        p2m_load_VTTBR(current->domain);
+        WRITE_SYSREG64(ovttbr, VTTBR_EL2);
+        isb();
         local_irq_restore(flags);
     }
 }
-- 
1.9.1


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