[Xen-devel] [PATCH] x86/vvmx: Fix nested virt on VMCS-Shadow capable hardware

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

c/s e9986b0dd "x86/vvmx: Simplify per-CPU memory allocations" had the wrong
indirection on its pointer check in nvmx_cpu_up_prepare(), causing the
VMCS-shadowing buffer never be allocated.  Fix it.

This in turn results in a massive quantity of logspam, as every virtual
vmentry/exit hits both gdprintk()s in the *_bulk() functions.

Switch these to using printk_once().  The size of the buffer is chosen at
compile time, so complaining about it repeatedly is of no benefit.

Finally, drop the runtime NULL pointer checks.  It is not terribly appropriate
to be repeatedly checking infrastructure which is set up from start-of-day,
and in this case, actually hid the above bug.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
CC: Kevin Tian <kevin.tian@xxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vvmx.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
index 332623d006..f38f3a9930 100644
--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -43,7 +43,7 @@ int nvmx_cpu_up_prepare(unsigned int cpu)
     uint64_t **vvmcs_buf;
 
     if ( cpu_has_vmx_vmcs_shadowing &&
-         (vvmcs_buf = &per_cpu(vvmcs_buf, cpu)) == NULL )
+         *(vvmcs_buf = &per_cpu(vvmcs_buf, cpu)) == NULL )
     {
         void *ptr = xzalloc_array(uint64_t, VMCS_BUF_SIZE);
 
@@ -922,11 +922,10 @@ static void vvmcs_to_shadow_bulk(struct vcpu *v, unsigned 
int n,
     if ( !cpu_has_vmx_vmcs_shadowing )
         goto fallback;
 
-    if ( !value || n > VMCS_BUF_SIZE )
+    if ( n > VMCS_BUF_SIZE )
     {
-        gdprintk(XENLOG_DEBUG, "vmcs sync fall back to non-bulk mode, "
-                 "buffer: %p, buffer size: %d, fields number: %d.\n",
-                 value, VMCS_BUF_SIZE, n);
+        printk_once(XENLOG_ERR "%pv VMCS sync too many fields %u\n",
+                    v, n);
         goto fallback;
     }
 
@@ -962,11 +961,10 @@ static void shadow_to_vvmcs_bulk(struct vcpu *v, unsigned 
int n,
     if ( !cpu_has_vmx_vmcs_shadowing )
         goto fallback;
 
-    if ( !value || n > VMCS_BUF_SIZE )
+    if ( n > VMCS_BUF_SIZE )
     {
-        gdprintk(XENLOG_DEBUG, "vmcs sync fall back to non-bulk mode, "
-                 "buffer: %p, buffer size: %d, fields number: %d.\n",
-                 value, VMCS_BUF_SIZE, n);
+        printk_once(XENLOG_ERR "%pv VMCS sync too many fields %u\n",
+                    v, n);
         goto fallback;
     }
 
-- 
2.11.0


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