Messages in this thread | | | Date | Wed, 7 Apr 2021 12:24:40 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v2 8/8] KVM: SVM: Allocate SEV command structures on local stack |
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First of all, I'd strongly suggest you trim your emails when you reply - that would be much appreciated.
On Wed, Apr 07, 2021 at 07:24:54AM +0200, Christophe Leroy wrote: > > @@ -258,7 +240,7 @@ static int sev_issue_cmd(struct kvm *kvm, int id, void *data, int *error) > > static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp) > > { > > struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info; > > - struct sev_data_launch_start *start; > > + struct sev_data_launch_start start; > > struct sev_data_launch_start start = {0, 0, 0, 0, 0, 0, 0};
I don't know how this is any better than using memset...
Also, you can do
... start = { };
which is certainly the only other alternative to memset, AFAIK.
But whatever you do, you need to look at the resulting asm the compiler generates. So let's do that:
Your version:
# arch/x86/kvm/svm/sev.c:261: struct sev_data_launch_start _tmp = {0, 0, 0, 0, 0, 0, 0}; movq $0, 104(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 112(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 120(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 128(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movl $0, 136(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
my version:
# arch/x86/kvm/svm/sev.c:261: struct sev_data_launch_start _tmp = {}; movq $0, 104(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 112(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 120(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movq $0, 128(%rsp) #, MEM[(struct sev_data_launch_start *)_561] movl $0, 136(%rsp) #, MEM[(struct sev_data_launch_start *)_561]
the memset version:
# arch/x86/kvm/svm/sev.c:269: memset(&_tmp, 0, sizeof(_tmp)); #NO_APP movq $0, 104(%rsp) #, MEM <char[1:36]> [(void *)_561] movq $0, 112(%rsp) #, MEM <char[1:36]> [(void *)_561] movq $0, 120(%rsp) #, MEM <char[1:36]> [(void *)_561] movq $0, 128(%rsp) #, MEM <char[1:36]> [(void *)_561] movl $0, 136(%rsp) #, MEM <char[1:36]> [(void *)_561]
Ok?
-- Regards/Gruss, Boris.
SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg
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