[Xen-devel] [PATCH 1/2] x86/xen: don't write ptes directly in 32-bit PV guests

[Juergen Gross <jgross@xxxxxxxx>]

In some cases 32-bit PAE PV guests still write PTEs directly instead of
using hypercalls. This is especially bad when clearing a PTE as this is
done via 32-bit writes which will produce intermediate L1TF attackable
PTEs.

Change the code to use hypercalls instead.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 arch/x86/xen/mmu_pv.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 9e7012858420..9396b4d17064 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -434,14 +434,13 @@ static void xen_set_pud(pud_t *ptr, pud_t val)
 static void xen_set_pte_atomic(pte_t *ptep, pte_t pte)
 {
        trace_xen_mmu_set_pte_atomic(ptep, pte);
-       set_64bit((u64 *)ptep, native_pte_val(pte));
+       __xen_set_pte(ptep, pte);
 }
 
 static void xen_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t 
*ptep)
 {
        trace_xen_mmu_pte_clear(mm, addr, ptep);
-       if (!xen_batched_set_pte(ptep, native_make_pte(0)))
-               native_pte_clear(mm, addr, ptep);
+       __xen_set_pte(ptep, native_make_pte(0));
 }
 
 static void xen_pmd_clear(pmd_t *pmdp)
@@ -1569,7 +1568,7 @@ static void __init xen_set_pte_init(pte_t *ptep, pte_t 
pte)
                pte = __pte_ma(((pte_val_ma(*ptep) & _PAGE_RW) | ~_PAGE_RW) &
                               pte_val_ma(pte));
 #endif
-       native_set_pte(ptep, pte);
+       __xen_set_pte(ptep, pte);
 }
 
 /* Early in boot, while setting up the initial pagetable, assume
-- 
2.13.7


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