Re: [Xen-devel] [PATCH SpectreV1+L1TF v6 5/9] nospec: introduce evaluate_nospec

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.02.19 at 14:44, <nmanthey@xxxxxxxxx> wrote:
> --- /dev/null
> +++ b/xen/include/asm-x86/nospec.h
> @@ -0,0 +1,39 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved. 
> */
> +
> +#ifndef _ASM_X86_NOSPEC_H
> +#define _ASM_X86_NOSPEC_H
> +
> +#include <asm/alternative.h>
> +#include <asm/system.h>
> +
> +/* Allow to insert a read memory barrier into conditionals */
> +static always_inline bool arch_barrier_nospec_true(void)

Now that this is x86-specific (and not used by common code),
I don't think the arch_ prefix is warranted anymore.

> +{
> +#if defined(CONFIG_HVM)

Here and below I'd prefer if you used the shorter #ifdef.

> +    alternative("", "lfence", X86_FEATURE_SC_L1TF_VULN);
> +#endif
> +    return true;
> +}
> +
> +/* Allow to protect evaluation of conditionaasl with respect to speculation 
> */
> +#if defined(CONFIG_HVM)
> +#define evaluate_nospec(condition)                                         \
> +    ((condition) ? arch_barrier_nospec_true() : !arch_barrier_nospec_true())
> +#else
> +#define evaluate_nospec(condition) (condition)
> +#endif
> +
> +/* Allow to block speculative execution in generic code */
> +#define block_speculation() (void)arch_barrier_nospec_true()

I'm pretty sure that I did point out before that this lacks an
outer pair of parentheses.

Jan



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