Re: [PATCH v6 01/19] i386: keep hyperv_vendor string up-to-date

[Vitaly Kuznetsov]

Eduardo Habkost <ehabkost@redhat.com> writes:

> On Thu, Apr 22, 2021 at 06:11:12PM +0200, Vitaly Kuznetsov wrote:
>> When cpu->hyperv_vendor is not set manually we default to "Microsoft Hv"
>> and in 'hv_passthrough' mode we get the information from the host. This
>> information is stored in cpu->hyperv_vendor_id[] array but we don't update
>> cpu->hyperv_vendor string so e.g. QMP's query-cpu-model-expansion output
>> is incorrect.
>
> I was confused for a while because this can't happen until patch
> 15/19 is applied.  Probably worth a note in the commit message
> indicating that hyperv_handle_properties() will be called by
> x86_cpu_expand_features() in the future.
>
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  target/i386/cpu.c     | 19 +++++++++----------
>>  target/i386/kvm/kvm.c |  5 +++++
>>  2 files changed, 14 insertions(+), 10 deletions(-)
>> 
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index ad99cad0e7ce..2d05df232329 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -6665,17 +6665,16 @@ static void x86_cpu_hyperv_realize(X86CPU *cpu)
>>  
>>      /* Hyper-V vendor id */
>>      if (!cpu->hyperv_vendor) {
>> -        memcpy(cpu->hyperv_vendor_id, "Microsoft Hv", 12);
>> -    } else {
>> -        len = strlen(cpu->hyperv_vendor);
>> -
>> -        if (len > 12) {
>> -            warn_report("hv-vendor-id truncated to 12 characters");
>> -            len = 12;
>> -        }
>> -        memset(cpu->hyperv_vendor_id, 0, 12);
>> -        memcpy(cpu->hyperv_vendor_id, cpu->hyperv_vendor, len);
>> +        object_property_set_str(OBJECT(cpu), "hv-vendor-id", "Microsoft Hv",
>> +                                &error_abort);
>> +    }
>> +    len = strlen(cpu->hyperv_vendor);
>> +    if (len > 12) {
>> +        warn_report("hv-vendor-id truncated to 12 characters");
>> +        len = 12;
>>      }
>> +    memset(cpu->hyperv_vendor_id, 0, 12);
>> +    memcpy(cpu->hyperv_vendor_id, cpu->hyperv_vendor, len);
>
> Existing issue: hardcoded 12 as the size of hyperv_vendor_id here
> (compare with the code you add below using sizeof()).  I don't
> think this should hold the whole series, so it can be fixed in a
> follow up patch if necessary.
>

Agreed, adding a patch to change '12' to sizeof().

>>  
>>      /* 'Hv#1' interface identification*/
>>      cpu->hyperv_interface_id[0] = 0x31237648;
>> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
>> index 7fe9f527103c..ab073a5e9c44 100644
>> --- a/target/i386/kvm/kvm.c
>> +++ b/target/i386/kvm/kvm.c
>> @@ -1215,6 +1215,11 @@ static int hyperv_handle_properties(CPUState *cs,
>>              cpu->hyperv_vendor_id[0] = c->ebx;
>>              cpu->hyperv_vendor_id[1] = c->ecx;
>>              cpu->hyperv_vendor_id[2] = c->edx;
>> +            cpu->hyperv_vendor = g_realloc(cpu->hyperv_vendor,
>> +                                           sizeof(cpu->hyperv_vendor_id) + 
>> 1);
>> +            memcpy(cpu->hyperv_vendor, cpu->hyperv_vendor_id,
>> +                   sizeof(cpu->hyperv_vendor_id));
>> +            cpu->hyperv_vendor[sizeof(cpu->hyperv_vendor_id)] = 0;
>
> I don't like having to do manual g_realloc() + memcpy() here
> (calling object_property_set_str() would be simpler), but I
> believe it will be easier to clean this up after this whole
> series is applied.

The problem here is that object_property_set_str() only works with
NULL-terminated strings and 'hyperv_vendor_id' doesn't have it (that's
why I explicitly do 'cpu->hyperv_vendor[sizeof(cpu->hyperv_vendor_id)] =
0'). We could've converted 'hyperv_vendor_id' to a char[13] array to
accomodate for '\0', but 

              cpu->hyperv_vendor_id[0] = c->ebx;
              cpu->hyperv_vendor_id[1] = c->ecx;
              cpu->hyperv_vendor_id[2] = c->edx;

assignments will have to be converted to something and this won't look
natural.

-- 
Vitaly