[xen staging] x86/nSVM: Ignore bits 11:0 of MSRPM_BASE_PA in L1's VMCB for L2

[patchbot@xxxxxxx]

commit 8d46c7de2d5294404b8f3e2334b4856a0bd0d29d
Author:     Stephen Cheng <stephen.cheng@xxxxxxxxxx>
AuthorDate: Tue Oct 27 09:00:49 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 27 09:00:49 2026 +0100

    x86/nSVM: Ignore bits 11:0 of MSRPM_BASE_PA in L1's VMCB for L2
    
    VMRUN ignores bits 11:0 of MSRPM_BASE_PA (APM volume 2, 24593 Rev. 3.44,
    section 15.11 "MSR Intercepts").  On L1's VMRUN of L2,
    nsvm_vmrun_permissionmap() copies the MSR permission map which L1 set up
    for L2 from MSRPM_BASE_PA exactly as L1 wrote it.  With any of those bits
    set, the copy starts at the wrong offset, so both the map L0 runs L2 with
    and the intercept check on #VMEXIT use the wrong bits: L1 can miss
    intercepts it set or see ones it didn't, and the copy may run into the
    following page, giving a spurious VMEXIT_INVALID if that isn't RAM.
    
    Mask the address before copying.
    
    Fixes: 9a779e4fc161 ("Implement SVM specific part for Nested 
Virtualization")
    Assisted-by: Claude:claude-opus-5-5
    Signed-off-by: Stephen Cheng <stephen.cheng@xxxxxxxxxx>
    Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/hvm/svm/nestedsvm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/svm/nestedsvm.c b/xen/arch/x86/hvm/svm/nestedsvm.c
index 2b998e26bc..56d0f0fa4d 100644
--- a/xen/arch/x86/hvm/svm/nestedsvm.c
+++ b/xen/arch/x86/hvm/svm/nestedsvm.c
@@ -309,8 +309,10 @@ static int nsvm_vmrun_permissionmap(struct vcpu *v)
 
     ns_msrpm_ptr = (unsigned long *)svm->ns_cached_msrpm;
 
+    /* VMRUN ignores bits 11:0 of MSRPM_BASE_PA. */
     ret = hvm_copy_from_guest_phys(svm->ns_cached_msrpm,
-                                   ns_vmcb->_msrpm_base_pa, MSRPM_SIZE);
+                                   ns_vmcb->_msrpm_base_pa & PAGE_MASK,
+                                   MSRPM_SIZE);
     if ( ret != HVMTRANS_okay )
     {
         gdprintk(XENLOG_ERR, "hvm_copy_from_guest_phys msrpm %u\n", ret);
--
generated by git-patchbot for /home/xen/git/xen.git#staging