[Xen-devel] [PATCH RFC 08/44] x86/pv: Avoid an opencoded mov to %cr3 in toggle_guest_mode()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Xen will need to track which %cr3 it is running on.  Propagate a
tlb_maintenance parameter down into write_ptbase(), so toggle_guest_mode() can
retain its optimisation of not flushing global mappings and not ticking the
TLB clock.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/mm.c               | 9 +++++++--
 xen/arch/x86/pv/domain.c        | 2 +-
 xen/include/asm-x86/processor.h | 6 +++++-
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 14cfa93..25f9588 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -497,9 +497,14 @@ void make_cr3(struct vcpu *v, mfn_t mfn)
     v->arch.cr3 = mfn_x(mfn) << PAGE_SHIFT;
 }
 
-void write_ptbase(struct vcpu *v)
+void do_write_ptbase(struct vcpu *v, bool tlb_maintenance)
 {
-    write_cr3(v->arch.cr3);
+    unsigned long new_cr3 = v->arch.cr3;
+
+    if ( tlb_maintenance )
+        write_cr3(new_cr3);
+    else
+        asm volatile ( "mov %0, %%cr3" :: "r" (new_cr3) : "memory" );
 }
 
 /*
diff --git a/xen/arch/x86/pv/domain.c b/xen/arch/x86/pv/domain.c
index 2234128..7e4566d 100644
--- a/xen/arch/x86/pv/domain.c
+++ b/xen/arch/x86/pv/domain.c
@@ -246,7 +246,7 @@ void toggle_guest_pt(struct vcpu *v)
     v->arch.flags ^= TF_kernel_mode;
     update_cr3(v);
     /* Don't flush user global mappings from the TLB. Don't tick TLB clock. */
-    asm volatile ( "mov %0, %%cr3" : : "r" (v->arch.cr3) : "memory" );
+    do_write_ptbase(v, false);
 
     if ( !(v->arch.flags & TF_kernel_mode) )
         return;
diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index a0c524b..c206080 100644
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -479,7 +479,11 @@ DECLARE_PER_CPU(struct tss_struct, init_tss);
 
 extern void init_int80_direct_trap(struct vcpu *v);
 
-extern void write_ptbase(struct vcpu *v);
+extern void do_write_ptbase(struct vcpu *v, bool tlb_maintenance);
+static inline void write_ptbase(struct vcpu *v)
+{
+    do_write_ptbase(v, true);
+}
 
 /* REP NOP (PAUSE) is a good thing to insert into busy-wait loops. */
 static always_inline void rep_nop(void)
-- 
2.1.4


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