[Xen-devel] [PATCHv2 1/3] x86/ept: remove unnecessary sync after resolving misconfigured entries

[David Vrabel <david.vrabel@xxxxxxxxxx>]

When using EPT, type changes are done with the following steps:

1. Set entry as invalid (misconfigured) by settings a reserved memory
type.

2. Flush all EPT and combined translations (ept_sync_domain()).

3. Fixup misconfigured entries as required (on EPT_MISCONFIG vmexits or
when explicitly setting an entry.

Since resolve_misconfig() only updates entries that were misconfigured,
there is no need to invalidate any translations since the hardware
does not cache misconfigured translations (vol 3, section 28.3.2).

Remove the unnecessary (and very expensive) ept_sync_domain() calls).

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
v2:
- remove needs_sync enum
---
 xen/arch/x86/mm/p2m-ept.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 86440fc..548f2f2 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -644,7 +644,6 @@ bool_t ept_handle_misconfig(uint64_t gpa)
     spurious = curr->arch.hvm_vmx.ept_spurious_misconfig;
     rc = resolve_misconfig(p2m, PFN_DOWN(gpa));
     curr->arch.hvm_vmx.ept_spurious_misconfig = 0;
-    ept_sync_domain(p2m);
 
     p2m_unlock(p2m);
 
@@ -671,7 +670,7 @@ ept_set_entry(struct p2m_domain *p2m, unsigned long gfn, 
mfn_t mfn,
     bool_t need_modify_vtd_table = 1;
     bool_t vtd_pte_present = 0;
     unsigned int iommu_flags = p2m_get_iommu_flags(p2mt);
-    enum { sync_off, sync_on, sync_check } needs_sync = sync_check;
+    bool_t needs_sync = 1;
     ept_entry_t old_entry = { .epte = 0 };
     ept_entry_t new_entry = { .epte = 0 };
     struct ept_data *ept = &p2m->ept;
@@ -692,12 +691,7 @@ ept_set_entry(struct p2m_domain *p2m, unsigned long gfn, 
mfn_t mfn,
     /* Carry out any eventually pending earlier changes first. */
     ret = resolve_misconfig(p2m, gfn);
     if ( ret < 0 )
-    {
-        ept_sync_domain(p2m);
         return ret;
-    }
-    if ( ret > 0 )
-        needs_sync = sync_on;
 
     ASSERT((target == 2 && hap_has_1gb) ||
            (target == 1 && hap_has_2mb) ||
@@ -740,8 +734,8 @@ ept_set_entry(struct p2m_domain *p2m, unsigned long gfn, 
mfn_t mfn,
         /* We reached the target level. */
 
         /* No need to flush if the old entry wasn't valid */
-        if ( needs_sync == sync_check && !is_epte_present(ept_entry) )
-            needs_sync = sync_off;
+        if ( !is_epte_present(ept_entry) )
+            needs_sync = 0;
 
         /* If we're replacing a non-leaf entry with a leaf entry (1GiB or 
2MiB),
          * the intermediate tables will be freed below after the ept flush
@@ -823,7 +817,7 @@ ept_set_entry(struct p2m_domain *p2m, unsigned long gfn, 
mfn_t mfn,
         p2m->max_mapped_pfn = gfn + (1UL << order) - 1;
 
 out:
-    if ( needs_sync != sync_off )
+    if ( needs_sync )
         ept_sync_domain(p2m);
 
     /* For host p2m, may need to change VT-d page table.*/
-- 
2.1.4


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