From: Andrew Cooper Date: Fri, 1 Sep 2017 11:15:39 +0000 (+0100) Subject: x86/mm: Always set _PAGE_ACCESSED on L4e updates X-Git-Tag: archive/raspbian/4.11.1-1+rpi1~1^2~66^2~836 X-Git-Url: https://dgit.raspbian.org/%22http:/www.example.com/cgi/%22https://%22%22/%22http:/www.example.com/cgi/%22https:/%22%22?a=commitdiff_plain;h=bd61fe94bee0556bc2f64999a4a8315b93f90f21;p=xen.git x86/mm: Always set _PAGE_ACCESSED on L4e updates Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- diff --git a/xen/arch/x86/pv/mm.h b/xen/arch/x86/pv/mm.h index 7502d533c6..976209ba4c 100644 --- a/xen/arch/x86/pv/mm.h +++ b/xen/arch/x86/pv/mm.h @@ -144,9 +144,21 @@ static inline l3_pgentry_t unadjust_guest_l3e(l3_pgentry_t l3e, static inline l4_pgentry_t adjust_guest_l4e(l4_pgentry_t l4e, const struct domain *d) { - if ( likely(l4e_get_flags(l4e) & _PAGE_PRESENT) && - likely(!is_pv_32bit_domain(d)) ) - l4e_add_flags(l4e, _PAGE_USER); + /* + * When shadowing an L4 behind the guests back (e.g. for per-pcpu + * purposes), we cannot efficiently sync access bit updates from hardware + * (on the shadow tables) back into the guest view. + * + * We therefore unconditionally set _PAGE_ACCESSED even in the guests + * view. This will appear to the guest as a CPU which proactively pulls + * all valid L4e's into its TLB, which is compatible with the x86 ABI. + * + * At the time of writing, all PV guests set the access bit anyway, so + * this is no actual change in their behaviour. + */ + if ( likely(l4e_get_flags(l4e) & _PAGE_PRESENT) ) + l4e_add_flags(l4e, (_PAGE_ACCESSED | + (is_pv_32bit_domain(d) ? 0 : _PAGE_USER))); return l4e; }