[PATCH v2] x86/hap: Defer NPT P2M TLB flushes

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

Like the EPT code, defer TLB flushes for NPT to reduce the number of
flushes and avoid holding the P2M lock while flushing. This can
substantially improve performance in some scenarios.

The cases where the TLB needs to be flushed without deferring are
already handled by the call to p2m_tlb_flush_sync() in p2m_free_ptp().

Suggested-by: Roger Pau Monne <roger.pau@xxxxxxxxxx>
Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
In v2:
* Tweak commit message.
* Call guest_flush_tlb_mask() if the assertion fails.

 xen/arch/x86/mm/hap/hap.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index a337752bf488..67137611d9db 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -814,15 +814,33 @@ static void cf_check hap_update_paging_modes(struct vcpu 
*v)
 static void cf_check
 hap_write_p2m_entry_post(struct p2m_domain *p2m, unsigned int oflags)
 {
-    struct domain *d = p2m->domain;
+    if ( !(oflags & _PAGE_PRESENT) )
+        return;
+
+    if ( unlikely(!p2m->defer_flush) )
+    {
+        struct domain *d = p2m->domain;
 
-    if ( oflags & _PAGE_PRESENT )
+        ASSERT_UNREACHABLE();
         guest_flush_tlb_mask(d, d->dirty_cpumask);
+        return;
+    }
+
+    p2m->need_flush = true;
+}
+
+static void cf_check
+hap_p2m_tlb_flush(struct p2m_domain *p2m)
+{
+    struct domain *d = p2m->domain;
+
+    guest_flush_tlb_mask(d, d->dirty_cpumask);
 }
 
 void hap_p2m_init(struct p2m_domain *p2m)
 {
     p2m->write_p2m_entry_post = hap_write_p2m_entry_post;
+    p2m->tlb_flush = hap_p2m_tlb_flush;
 }
 
 static unsigned long cf_check hap_gva_to_gfn_real_mode(
-- 
2.53.0