[PATCH v1 1/6] nestedsvm: Fix CR3 MBZ check

[Ross Lagerwall <ross.lagerwall@citrix.com>]

The existing code checks for any reserved bit set while the APM only
considers it invalid if an MBZ bit is set. Relax the check to match the
APM and hardware.

Some of the reserved bits were observed to be set running Rocky Linux
10.1 on Xen on Xen.

Fixes: 9a779e4fc161 ("Implement SVM specific part for Nested Virtualization")
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
---
 xen/arch/x86/hvm/svm/vmcb.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/vmcb.c b/xen/arch/x86/hvm/svm/vmcb.c
index 975a1eaef806..9ada491e57db 100644
--- a/xen/arch/x86/hvm/svm/vmcb.c
+++ b/xen/arch/x86/hvm/svm/vmcb.c
@@ -347,10 +347,8 @@ bool svm_vmcb_isvalid(
         PRINTF("CR0: bits [63:32] are not zero (%#"PRIx64")\n", cr0);
 
     if ( (cr0 & X86_CR0_PG) &&
-         ((cr3 & 7) ||
-          ((!(cr4 & X86_CR4_PAE) || (efer & EFER_LMA)) && (cr3 & 0xfe0)) ||
-          ((efer & EFER_LMA) &&
-           (cr3 >> v->domain->arch.cpuid->extd.maxphysaddr))) )
+         ((efer & EFER_LMA) &&
+           (cr3 >> v->domain->arch.cpuid->extd.maxphysaddr)) )
         PRINTF("CR3: MBZ bits are set (%#"PRIx64")\n", cr3);
 
     valid = hvm_cr4_guest_valid_bits(v->domain);
-- 
2.53.0