[xen master] x86/np2m: flush the np2m on an SVM nested TLB flush

[patchbot@xxxxxxx]

commit 5e529e4e7b1a0b27f25017e18e8665e864b72fdb
Author:     Stephen Cheng <stephen.cheng@xxxxxxxxxx>
AuthorDate: Tue Oct 27 08:57:45 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 27 08:57:45 2026 +0100

    x86/np2m: flush the np2m on an SVM nested TLB flush
    
    On SVM, L1 flushes what is cached from its nested page tables by setting
    TLB_CONTROL or using a new ASID on VMRUN.  Either sets nv_flushp2m, which
    p2m_get_nestedp2m_locked() handles by only dropping nv_p2m.  Since np2ms
    are shared between vCPUs, the lookup then finds the np2m for the same
    N_CR3 and reuses it as is, so L2 keeps the mappings from before L1 changed
    its NPT.
    
    The obvious fix, flushing nv_p2m (the np2m this vCPU used last) before
    dropping it, is not enough.  It covers a vCPU re-entering the same N_CR3,
    but not one entering an N_CR3 whose np2m another vCPU filled: on its
    first VMRUN (nv_p2m is NULL), with an ASID new to it, or when switching
    N_CR3.
    
    Instead, flush the np2m for the incoming N_CR3 before reusing it, as
    nested VMX does via np2m_flush_base() on INVEPT.
    
    Fixes: 6df4b481b0c5 ("x86/np2m: implement sharing of np2m between vCPUs")
    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/mm/p2m.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 027b9ae69b..52cadd9b25 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1547,7 +1547,11 @@ p2m_get_nestedp2m_locked(struct vcpu *v)
         p2m_lock(p2m);
 
         if ( p2m->np2m_base == np2m_base )
+        {
+            if ( nv->nv_flushp2m )
+                p2m_flush_table_locked(p2m);
             goto found;
+        }
 
         p2m_unlock(p2m);
     }
--
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