On 06/09/2019 16:18, Jan Beulich wrote:
> On 05.09.2019 21:49, Andrew Cooper wrote:
>> --- a/xen/arch/x86/cpuid.c
>> +++ b/xen/arch/x86/cpuid.c
>> @@ -21,45 +21,62 @@ static const uint32_t deep_features[] =
>> INIT_DEEP_FEATURES;
>>
>> static int __init parse_xen_cpuid(const char *s)
>> {
>> + static const struct feature {
>> + const char *name;
>> + unsigned int bit;
>> + } features[] __initconst = INIT_FEATURE_NAMES, *lhs, *mid, *rhs;
> The pointer field want this to use __initconstrel.
Ok.
> And I don't think you mean lhs, mid, and rhs to also be static?
No - not intentional.
> Albeit ...
>
>> const char *ss;
>> int val, rc = 0;
>>
>> do {
>> + const char *feat;
>> +
>> ss = strchr(s, ',');
>> if ( !ss )
>> ss = strchr(s, '\0');
>>
>> - if ( (val = parse_boolean("md-clear", s, ss)) >= 0 )
>> - {
>> - if ( !val )
>> - setup_clear_cpu_cap(X86_FEATURE_MD_CLEAR);
>> - }
>> - else if ( (val = parse_boolean("ibpb", s, ss)) >= 0 )
>> - {
>> - if ( !val )
>> - setup_clear_cpu_cap(X86_FEATURE_IBPB);
>> - }
>> - else if ( (val = parse_boolean("ibrsb", s, ss)) >= 0 )
>> - {
>> - if ( !val )
>> - setup_clear_cpu_cap(X86_FEATURE_IBRSB);
>> - }
>> - else if ( (val = parse_boolean("stibp", s, ss)) >= 0 )
>> - {
>> - if ( !val )
>> - setup_clear_cpu_cap(X86_FEATURE_STIBP);
>> - }
>> - else if ( (val = parse_boolean("l1d-flush", s, ss)) >= 0 )
>> - {
>> - if ( !val )
>> - setup_clear_cpu_cap(X86_FEATURE_L1D_FLUSH);
>> - }
>> - else if ( (val = parse_boolean("ssbd", s, ss)) >= 0 )
>> + /* Skip the 'no-' prefix for name comparisons. */
>> + feat = s;
>> + if ( strncmp(s, "no-", 3) == 0 )
>> + feat += 3;
>> +
>> + /* (Re)initalise lhs and rhs for binary search. */
>> + lhs = features;
>> + rhs = features + ARRAY_SIZE(features);
> ... the comment here suggests you do, but I don't currently see why.
We are inside a do { } () while loop, parsing something such as
cpuid=avx512,ss,smx
The binary search over the feature names needs to start again from
scratch for each new cpuid= list item.
Otherwise, the while ( lhs < rhs ) binary search will never be entered
for the second cpuid= item.
~Andrew
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