Messages in this thread | | | From | "Huang, Kai" <> | Subject | Re: [PATCH 3/3] KVM: x86: Explicitly zero kvm_caps during vendor module load | Date | Wed, 24 Apr 2024 03:25:45 +0000 |
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On Tue, 2024-04-23 at 09:53 -0700, Sean Christopherson wrote: > Zero out all of kvm_caps when loading a new vendor module to ensure that > KVM can't inadvertently rely on global initialization of a field, and add > a comment above the definition of kvm_caps to call out that all fields > needs to be explicitly computed during vendor module load. > > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/x86.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 44ce187bad89..8f3979d5fc80 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -92,6 +92,11 @@ > #define MAX_IO_MSRS 256 > #define KVM_MAX_MCE_BANKS 32 > > +/* > + * Note, kvm_caps fields should *never* have default values, all fields must be > + * recomputed from scratch during vendor module load, e.g. to account for a > + * vendor module being reloaded with different module parameters. > + */ > struct kvm_caps kvm_caps __read_mostly; > EXPORT_SYMBOL_GPL(kvm_caps); > > @@ -9755,6 +9760,8 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops) > return -EIO; > } > > + memset(&kvm_caps, 0, sizeof(kvm_caps)); > + > x86_emulator_cache = kvm_alloc_emulator_cache(); > if (!x86_emulator_cache) { > pr_err("failed to allocate cache for x86 emulator\n");
Why do the memset() here particularly?
Isn't it better to put ...
memset(&kvm_caps, 0, sizeof(kvm_caps)); kvm_caps.supported_vm_types = BIT(KVM_X86_DEFAULT_VM); kvm_caps.supported_mce_cap = MCG_CTL_P | MCG_SER_P;
... together so it can be easily seen?
We can even have a helper to do above to "reset kvm_caps to default values" I think.
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