[xen staging] x86/PV: guest_get_eff_kern_l1e() may still need to switch page tables

[patchbot@xxxxxxx]

commit 904148ecb4a59d4c8375d8e8d38117b8605e10ac
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Dec 15 13:47:45 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Dec 15 13:47:45 2020 +0100

    x86/PV: guest_get_eff_kern_l1e() may still need to switch page tables
    
    While indeed unnecessary for pv_ro_page_fault(), pv_map_ldt_shadow_page()
    may run when guest user mode is active, and hence may need to switch to
    the kernel page tables in order to retrieve an LDT page mapping.
    
    Fixes: 9ff970564764 ("x86/mm: drop guest_get_eff_l1e()")
    Reported-by: Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Tested-by: Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/pv/mm.h | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/pv/mm.h b/xen/arch/x86/pv/mm.h
index 2a21859dd4..62b1194e87 100644
--- a/xen/arch/x86/pv/mm.h
+++ b/xen/arch/x86/pv/mm.h
@@ -11,10 +11,15 @@ int new_guest_cr3(mfn_t mfn);
  */
 static inline l1_pgentry_t guest_get_eff_kern_l1e(unsigned long linear)
 {
+    struct vcpu *curr = current;
+    bool user_mode = !(curr->arch.flags & TF_kernel_mode);
     l1_pgentry_t l1e;
 
-    ASSERT(!paging_mode_translate(current->domain));
-    ASSERT(!paging_mode_external(current->domain));
+    ASSERT(!paging_mode_translate(curr->domain));
+    ASSERT(!paging_mode_external(curr->domain));
+
+    if ( user_mode )
+        toggle_guest_pt(curr);
 
     if ( unlikely(!__addr_ok(linear)) ||
          __copy_from_user(&l1e,
@@ -22,6 +27,9 @@ static inline l1_pgentry_t guest_get_eff_kern_l1e(unsigned 
long linear)
                           sizeof(l1_pgentry_t)) )
         l1e = l1e_empty();
 
+    if ( user_mode )
+        toggle_guest_pt(curr);
+
     return l1e;
 }
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging