Re: [Xen-devel] [PATCH SpectreV1+L1TF v7 4/9] nospec: introduce evaluate_nospec

[Norbert Manthey <nmanthey@xxxxxxxxx>]

On 2/22/19 14:17, Jan Beulich wrote:
>>>> On 21.02.19 at 09:16, <nmanthey@xxxxxxxxx> wrote:
>> --- /dev/null
>> +++ b/xen/include/asm-x86/nospec.h
>> @@ -0,0 +1,38 @@
>> +/* 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>
>> +
>> +/* Allow to insert a read memory barrier into conditionals */
>> +static always_inline bool barrier_nospec_true(void)
>> +{
>> +#ifdef CONFIG_HVM
>> +    alternative("", "lfence", X86_FEATURE_SC_L1TF_VULN);
>> +#endif
>> +    return true;
>> +}
>> +
>> +/* Allow to protect evaluation of conditionasl with respect to speculation 
>> */
>> +#ifdef CONFIG_HVM
>> +#define evaluate_nospec(condition)                                         \
>> +    ((condition) ? barrier_nospec_true() : !barrier_nospec_true())
>> +#else
>> +#define evaluate_nospec(condition) (condition)
>> +#endif
>> +
>> +/* Allow to block speculative execution in generic code */
>> +#define block_speculation() ((void)barrier_nospec_true())
> Seeing Julien's request for switching to inline functions on the Arm side,
> is there anything preventing these two to become inline functions too?

No, there is nothing preventing using functions here. I mostly copied
the macro style from other nospec constructs. I tested the generated
binary for the functions being always_inline, and the result is the same
as when using macros. I will turn the macros into functions that use the
always_inline keyword, as there have been problems with the
barrier_nospec_true function when not using always_inline.

Best,
Norbert




Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrer: Christian Schlaeger, Ralf Herbrich
Ust-ID: DE 289 237 879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel