Re: [Xen-devel] [PATCH 4/5] xen/vm_event: Deny MSR writes if refused by vm_event reply

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.05.15 at 19:12, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> --- a/xen/include/asm-x86/domain.h
> +++ b/xen/include/asm-x86/domain.h
> @@ -518,6 +518,11 @@ struct arch_vcpu
>          struct vm_event_emul_read_data emul_read_data;
>      } vm_event;
>  
> +    struct {
> +        bool_t do_write;
> +        uint64_t msr;
> +        uint64_t value;
> +    } msr_write;
>  };

Again a growth of struct vcpu by 24 bytes for everyone even though
quite likely only very few VMs would actually need this. To be honest
I'd even be hesitant to accept a pointer addition here. Perhaps this
should be a suitably sized, dynamically allocated array hanging off of
struct domain?

> --- a/xen/include/public/vm_event.h
> +++ b/xen/include/public/vm_event.h
> @@ -158,6 +158,11 @@ struct vm_event_regs_x86 {
>   * MEM_ACCESS_EMULATE_NOWRITE.
>   */
>  #define MEM_ACCESS_SET_EMUL_READ_DATA   (1 << 8)
> + /*
> +  * If mov_to_msr events are enabled, setting this flag in the vm_event
> +  * response denies the MSR write that triggered the event.
> +  */
> +#define MEM_ACCESS_SKIP_MSR_WRITE       (1 << 9)

From an interface point of view - does this need to be MSR-
specific? I.e. can't this just be a flag to deny whatever the
operation was (not necessarily supported/valid for all events,
but possibly for more than just MSR writes)?

Jan


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