Re: [Qemu-devel] [PATCH 3/3] i386/kvm: initialize struct at full before ioctl call

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 30.07.19 21:20, Paolo Bonzini wrote:
> On 30/07/19 18:01, Andrey Shinkevich wrote:
>> Not the whole structure is initialized before passing it to the KVM.
>> Reduce the number of Valgrind reports.
>>
>> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> 
> Christian, is this the right fix?  It's not expensive so it wouldn't be
> an issue, just checking if there's any better alternative.

I think all of these variants are valid with pros and cons
1. teach valgrind about this:
Add to coregrind/m_syswrap/syswrap-linux.c (and the relevant header files)
knowledge about which parts are actually touched.
2. use designated initializers
3. use memset
3. use a valgrind callback VG_USERREQ__MAKE_MEM_DEFINED to tell that this memory is defined

> 
> Paolo
> 
>> ---
>>  target/i386/kvm.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
>> index dbbb137..ed57e31 100644
>> --- a/target/i386/kvm.c
>> +++ b/target/i386/kvm.c
>> @@ -190,6 +190,7 @@ static int kvm_get_tsc(CPUState *cs)
>>          return 0;
>>      }
>>  
>> +    memset(&msr_data, 0, sizeof(msr_data));
>>      msr_data.info.nmsrs = 1;
>>      msr_data.entries[0].index = MSR_IA32_TSC;
>>      env->tsc_valid = !runstate_is_running();
>> @@ -1706,6 +1707,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
>>  
>>      if (has_xsave) {
>>          env->xsave_buf = qemu_memalign(4096, sizeof(struct kvm_xsave));
>> +        memset(env->xsave_buf, 0, sizeof(struct kvm_xsave));
>>      }
>>  
>>      max_nested_state_len = kvm_max_nested_state_length();
>> @@ -3477,6 +3479,7 @@ static int kvm_put_debugregs(X86CPU *cpu)
>>          return 0;
>>      }
>>  
>> +    memset(&dbgregs, 0, sizeof(dbgregs));
>>      for (i = 0; i < 4; i++) {
>>          dbgregs.db[i] = env->dr[i];
>>      }
>> -- 
>> 1.8.3.1
>>
> 
>