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

Christian Borntraeger
2019-07-30T17:05:30Z

On 30.07.19 18:44, Philippe Mathieu-Daudé wrote:
> On 7/30/19 6:01 PM, 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>
>> ---
>> 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));
>
> I wonder the overhead of this one...

Cant we use designated initializers like in

commit bdfc8480c50a53d91aa9a513d23a84de0d5fbc86
Author: Christian Borntraeger <borntraeger@de.ibm.com>
AuthorDate: Thu Oct 30 09:23:41 2014 +0100
Commit: Paolo Bonzini <pbonzini@redhat.com>
CommitDate: Mon Dec 15 12:21:01 2014 +0100

valgrind/i386: avoid false positives on KVM_SET_XCRS ioctl

and others?

This should minimize the impact.
>
>> 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));
>
> OK
>
>> }
>>
>> 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));
>
> OK
>
>> for (i = 0; i < 4; i++) {
>> dbgregs.db[i] = env->dr[i];
>> }
>
> We could remove 'dbgregs.flags = 0;'
>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>