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@xxxxxxxxxx>
> ---
> 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.
