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SubjectRe: [PATCH 4.14 103/115] x86/xen: dont write ptes directly in 32-bit PV guests
Hello,

On Thu, Sep 13, 2018 at 03:32:03PM +0200, Greg Kroah-Hartman wrote:
> 4.14-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Juergen Gross <jgross@suse.com>
>
> commit f7c90c2aa4004808dff777ba6ae2c7294dd06851 upstream.
>
> 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.
>

Good that we got this in. Should we also take this one:
b2d7a075a1cc ("x86/pae: use 64 bit atomic xchg function in native_ptep_get_and_clear")

Which is under the line of the same issue?

> Signed-off-by: Juergen Gross <jgross@suse.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
> arch/x86/xen/mmu_pv.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> --- a/arch/x86/xen/mmu_pv.c
> +++ b/arch/x86/xen/mmu_pv.c
> @@ -425,14 +425,13 @@ static void xen_set_pud(pud_t *ptr, pud_
> 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)
> @@ -1543,7 +1542,7 @@ static void __init xen_set_pte_init(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
>
>
>

--
All the best,
Eduardo Valentin

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