[Xen-changelog] [xen staging] xen/arm: p2m: Only use isb() when it is necessary

[patchbot@xxxxxxx]

commit 60bb42bb7569596a7141e73eff8029a401e591cb
Author:     Julien Grall <julien.grall@xxxxxxx>
AuthorDate: Mon Jan 28 11:50:24 2019 +0000
Commit:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
CommitDate: Mon Jan 28 16:53:59 2019 -0800

    xen/arm: p2m: Only use isb() when it is necessary
    
    The EL1 translation regime is out-of-context when running at EL2. This
    means the processor cannot speculate memory accesses using the registers
    associated to that regime.
    
    An isb() is only needed if Xen is going to use the translation regime
    before returning to the guest (exception returns will synchronize the
    context).
    
    Remove unnecessary isb() and document the ones left.
    
    Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
    Reviewed-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/p2m.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 9844bfb936..44391a5f8c 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -106,17 +106,21 @@ void p2m_restore_state(struct vcpu *n)
         return;
 
     WRITE_SYSREG64(p2m->vttbr, VTTBR_EL2);
-    isb();
-
     WRITE_SYSREG(n->arch.sctlr, SCTLR_EL1);
-    isb();
-
     WRITE_SYSREG(n->arch.hcr_el2, HCR_EL2);
-    isb();
 
     last_vcpu_ran = &p2m->last_vcpu_ran[smp_processor_id()];
 
     /*
+     * While we are restoring an out-of-context translation regime
+     * we still need to ensure:
+     *  - VTTBR_EL2 is synchronized before flushing the TLBs
+     *  - All registers for EL1 are synchronized before executing an AT
+     *  instructions targeting S1/S2.
+     */
+    isb();
+
+    /*
      * Flush local TLB for the domain to prevent wrong TLB translation
      * when running multiple vCPU of the same domain on a single pCPU.
      */
@@ -147,6 +151,7 @@ static void p2m_force_tlb_flush_sync(struct p2m_domain *p2m)
     {
         local_irq_save(flags);
         WRITE_SYSREG64(p2m->vttbr, VTTBR_EL2);
+        /* Ensure VTTBR_EL2 is synchronized before flushing the TLBs */
         isb();
     }
 
@@ -155,6 +160,7 @@ static void p2m_force_tlb_flush_sync(struct p2m_domain *p2m)
     if ( ovttbr != READ_SYSREG64(VTTBR_EL2) )
     {
         WRITE_SYSREG64(ovttbr, VTTBR_EL2);
+        /* Ensure VTTBR_EL2 is back in place before continuing. */
         isb();
         local_irq_restore(flags);
     }
@@ -1907,7 +1913,6 @@ static uint32_t __read_mostly vtcr;
 static void setup_virt_paging_one(void *data)
 {
     WRITE_SYSREG32(vtcr, VTCR_EL2);
-    isb();
 }
 
 void __init setup_virt_paging(void)
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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