From: Jan Beulich Date: Thu, 25 Feb 2021 14:39:09 +0000 (+0100) Subject: x86/PV: use get_unsafe() instead of copy_from_unsafe() X-Git-Tag: archive/raspbian/4.16.0+51-g0941d6cb-1+rpi1~2^2~42^2~867 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=972cd4308775f4eb48cbba3cc4efaf39e55c8057;p=xen.git x86/PV: use get_unsafe() instead of copy_from_unsafe() The former expands to a single (memory accessing) insn, which the latter does not guarantee (the __builtin_constant_p() based switch() statement there is just an optimization). Yet we'd prefer to read consistent PTEs rather than risking a split read racing with an update done elsewhere. Signed-off-by: Jan Beulich Reviewed-by: Roger Pau Monné Release-Acked-by: Ian Jackson --- diff --git a/xen/arch/x86/pv/mm.c b/xen/arch/x86/pv/mm.c index cb86143832..5ed7b3ccdb 100644 --- a/xen/arch/x86/pv/mm.c +++ b/xen/arch/x86/pv/mm.c @@ -41,9 +41,7 @@ l1_pgentry_t *map_guest_l1e(unsigned long linear, mfn_t *gl1mfn) return NULL; /* Find this l1e and its enclosing l1mfn in the linear map. */ - if ( copy_from_unsafe(&l2e, - &__linear_l2_table[l2_linear_offset(linear)], - sizeof(l2_pgentry_t)) ) + if ( get_unsafe(l2e, &__linear_l2_table[l2_linear_offset(linear)]) ) return NULL; /* Check flags that it will be safe to read the l1e. */ diff --git a/xen/arch/x86/pv/mm.h b/xen/arch/x86/pv/mm.h index 7e2259c488..5a117c735d 100644 --- a/xen/arch/x86/pv/mm.h +++ b/xen/arch/x86/pv/mm.h @@ -22,9 +22,7 @@ static inline l1_pgentry_t guest_get_eff_kern_l1e(unsigned long linear) toggle_guest_pt(curr); if ( unlikely(!__addr_ok(linear)) || - copy_from_unsafe(&l1e, - &__linear_l1_table[l1_linear_offset(linear)], - sizeof(l1_pgentry_t)) ) + get_unsafe(l1e, &__linear_l1_table[l1_linear_offset(linear)]) ) l1e = l1e_empty(); if ( user_mode )