Re: [Xen-devel] [PATCH v4 1/6] microcode/intel: extend microcode_update_match()

[Chao Gao <chao.gao@xxxxxxxxx>]

On Wed, Nov 28, 2018 at 11:58:06AM +0100, Roger Pau Monné wrote:
>On Wed, Nov 28, 2018 at 01:34:11PM +0800, Chao Gao wrote:
>> to a more generic function. The benefit is that this function can be
>> used to check whether a microcode is newer than another as well. We
>> rely on this function to decide to perform a replacement or an add when
>> updating the global microcode cache (introduced by later patches in
>> this series).
>> 
>> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
>> ---
>>  xen/arch/x86/microcode_intel.c | 57 
>> +++++++++++++++++++++++-------------------
>>  1 file changed, 31 insertions(+), 26 deletions(-)
>> 
>> diff --git a/xen/arch/x86/microcode_intel.c b/xen/arch/x86/microcode_intel.c
>> index 9657575..8d9a3b2 100644
>> --- a/xen/arch/x86/microcode_intel.c
>> +++ b/xen/arch/x86/microcode_intel.c
>> @@ -127,14 +127,37 @@ static int collect_cpu_info(unsigned int cpu_num, 
>> struct cpu_signature *csig)
>>      return 0;
>>  }
>>  
>> -static inline int microcode_update_match(
>> -    unsigned int cpu_num, const struct microcode_header_intel *mc_header,
>> -    int sig, int pf)
>> +enum {
>> +    OLD_UCODE, /* signature matched, but revision id isn't newer */
>> +    NEW_UCODE, /* signature matched, but revision id is newer */
>> +    MIS_UCODE, /* signature mismatched */
>> +};
>
>Shouldn't you give a name to this type ...
>
>> +static int microcode_update_match(const void *mc,
>
>... so that this function can return it instead of int?
>
>> +        unsigned int sig, unsigned int pf, unsigned int rev)
>>  {
>> -    struct ucode_cpu_info *uci = &per_cpu(ucode_cpu_info, cpu_num);
>> +    const struct microcode_header_intel *mc_header = mc;
>> +    const struct extended_sigtable *ext_header;
>> +    unsigned long total_size = get_totalsize(mc_header);
>
>size_t might be more appropriate here.
>
>> +    int ext_sigcount, i;
>
>unsigned int.
>
>> +    struct extended_signature *ext_sig;
>
>const?
>
>>  
>> -    return (sigmatch(sig, uci->cpu_sig.sig, pf, uci->cpu_sig.pf) &&
>> -            (mc_header->rev > uci->cpu_sig.rev));
>> +    if ( sigmatch(sig, mc_header->sig, pf, mc_header->pf) )
>> +        return (mc_header->rev > rev) ? NEW_UCODE : OLD_UCODE;
>> +
>> +    if ( total_size <= (get_datasize(mc_header) + MC_HEADER_SIZE) )
>> +        return MIS_UCODE;
>
>Shouldn't you perform this check before the signature check?

I think this check shouldn't be here. Given that this check is also
done in microcode_sanity_check(), I will remove this check here.

>
>> +
>> +    ext_header = mc + get_datasize(mc_header) + MC_HEADER_SIZE;
>> +    ext_sigcount = ext_header->count;
>> +    ext_sig = (void *)ext_header + EXT_HEADER_SIZE;
>
>You are dropping the const here AFAICT by casting to void *.
>
>> +    for ( i = 0; i < ext_sigcount; i++ )
>> +    {
>> +        if ( sigmatch(sig, ext_sig->sig, pf, ext_sig->pf) )
>> +            return (mc_header->rev > rev) ? NEW_UCODE : OLD_UCODE;
>> +        ext_sig++;
>> +    }
>
>I would add a newline here for readability.
>
>> +    return MIS_UCODE;
>>  }
>>  
>>  static int microcode_sanity_check(void *mc)
>> @@ -236,31 +259,13 @@ static int get_matching_microcode(const void *mc, 
>> unsigned int cpu)
>>  {
>>      struct ucode_cpu_info *uci = &per_cpu(ucode_cpu_info, cpu);
>>      const struct microcode_header_intel *mc_header = mc;
>> -    const struct extended_sigtable *ext_header;
>>      unsigned long total_size = get_totalsize(mc_header);
>> -    int ext_sigcount, i;
>> -    struct extended_signature *ext_sig;
>>      void *new_mc;
>>  
>> -    if ( microcode_update_match(cpu, mc_header,
>> -                                mc_header->sig, mc_header->pf) )
>> -        goto find;
>> -
>> -    if ( total_size <= (get_datasize(mc_header) + MC_HEADER_SIZE) )
>> +    if ( microcode_update_match(mc, uci->cpu_sig.sig, uci->cpu_sig.pf,
>> +                                uci->cpu_sig.rev) != NEW_UCODE )
>>          return 0;
>
>Shouldn't you differentiate between the function returning OLD_UCODE
>or MIS_UCODE? I would expect that trying to load a mismatched UCODE
>would trigger some kind of message from Xen.

I don't differentiate these two cases. For both of them, we do nothing.
Actually, I add a message "No newer or matched microcode found" in patch 4
for them (Currently each cpu parses the file locally, if we add
an error message, it will show up many times). However, if you are to load
a corrupted file, another error will be prompted.

Other comments are fine with me.

Thanks
Chao

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