[PATCH kvm-unit-tests 0/2] access: cut more execution time on reserved bit tests

[PATCH kvm-unit-tests 0/2] access: cut more execution time on reserved bit tests

[Paolo Bonzini]

Cut execution time by another 25%, from ~4 minutes to 2:40.

Paolo Bonzini (2):
  access: optimize check for multiple reserved bits
  access: treat NX as reserved if EFER.NXE=0

 x86/access.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

-- 
2.27.0

[PATCH kvm-unit-tests 1/2] access: optimize check for multiple reserved bits

[Paolo Bonzini]

Instead of using multiple ANDs statements, build a mask and check
it for more than one set bit.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 x86/access.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/x86/access.c b/x86/access.c
index c71f39d..6285c8c 100644
--- a/x86/access.c
+++ b/x86/access.c
@@ -288,6 +288,7 @@ static int ac_test_bump_one(ac_test_t *at)
 static _Bool ac_test_legal(ac_test_t *at)
 {
     int flags = at->flags;
+    unsigned reserved;
 
     if (F(AC_ACCESS_FETCH) && F(AC_ACCESS_WRITE))
 	return false;
@@ -321,8 +322,12 @@ static _Bool ac_test_legal(ac_test_t *at)
      * error code; the odds of a KVM bug are super low, and the odds of actually
      * being able to detect a bug are even lower.
      */
-    if ((F(AC_PDE_BIT51) + F(AC_PDE_BIT36) + F(AC_PDE_BIT13) +
-        F(AC_PTE_BIT51) + F(AC_PTE_BIT36)) > 1)
+    reserved = (AC_PDE_BIT51_MASK | AC_PDE_BIT36_MASK | AC_PDE_BIT13_MASK |
+	        AC_PTE_BIT51_MASK | AC_PTE_BIT36_MASK);
+
+    /* Only test one reserved bit at a time.  */
+    reserved &= flags;
+    if (reserved & (reserved - 1))
         return false;
 
     return true;
-- 
2.27.0

[PATCH kvm-unit-tests 2/2] access: treat NX as reserved if EFER.NXE=0

[Paolo Bonzini]

Cull more tests if EFER.NXE=0.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 x86/access.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/x86/access.c b/x86/access.c
index 6285c8c..4725bbd 100644
--- a/x86/access.c
+++ b/x86/access.c
@@ -324,6 +324,8 @@ static _Bool ac_test_legal(ac_test_t *at)
      */
     reserved = (AC_PDE_BIT51_MASK | AC_PDE_BIT36_MASK | AC_PDE_BIT13_MASK |
 	        AC_PTE_BIT51_MASK | AC_PTE_BIT36_MASK);
+    if (!F(AC_CPU_EFER_NX))
+        reserved |= AC_PDE_NX_MASK | AC_PTE_NX_MASK;
 
     /* Only test one reserved bit at a time.  */
     reserved &= flags;
-- 
2.27.0

Re: [PATCH kvm-unit-tests 0/2] access: cut more execution time on reserved bit tests

[Babu Moger]

On 8/13/21 6:12 AM, Paolo Bonzini wrote:
> Cut execution time by another 25%, from ~4 minutes to 2:40.
> 
> Paolo Bonzini (2):
>   access: optimize check for multiple reserved bits
>   access: treat NX as reserved if EFER.NXE=0
> 
>  x86/access.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 

Tested-by: Babu Moger <babu.moger@amd.com>

Looks good. Number of tests reduced by half.

Before the patch.

#./tests/access
enabling apic
starting test

run
41287685 tests, 0 failures
PASS access
===========================================
After the patch.

# time ./tests/access

run
28753925 tests, 0 failures
PASS access

Thanks
Babu