Re: [PATCH 12/15] KVM: x86: Export the number of uret MSRs to vendor modules

[Maxim Levitsky]

On Tue, 2021-05-04 at 10:17 -0700, Sean Christopherson wrote:
> Split out and export the number of configured user return MSRs so that
> VMX can iterate over the set of MSRs without having to do its own tracking.
> Keep the list itself internal to x86 so that vendor code still has to go
> through the "official" APIs to add/modify entries.
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/kvm_host.h |  1 +
>  arch/x86/kvm/x86.c              | 29 +++++++++++++----------------
>  2 files changed, 14 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index c9452472ed55..10663610f105 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1419,6 +1419,7 @@ struct kvm_arch_async_pf {
>  	bool direct_map;
>  };
>  
> +extern u32 __read_mostly kvm_nr_uret_msrs;
>  extern u64 __read_mostly host_efer;
>  extern bool __read_mostly allow_smaller_maxphyaddr;
>  extern struct kvm_x86_ops kvm_x86_ops;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 90ef340565a4..2fd46e917666 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -184,11 +184,6 @@ module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR);
>   */
>  #define KVM_MAX_NR_USER_RETURN_MSRS 16
>  
> -struct kvm_user_return_msrs_global {
> -	int nr;
> -	u32 msrs[KVM_MAX_NR_USER_RETURN_MSRS];
> -};
> -
>  struct kvm_user_return_msrs {
>  	struct user_return_notifier urn;
>  	bool registered;
> @@ -198,7 +193,9 @@ struct kvm_user_return_msrs {
>  	} values[KVM_MAX_NR_USER_RETURN_MSRS];
>  };
>  
> -static struct kvm_user_return_msrs_global __read_mostly user_return_msrs_global;
> +u32 __read_mostly kvm_nr_uret_msrs;
> +EXPORT_SYMBOL_GPL(kvm_nr_uret_msrs);
> +static u32 __read_mostly kvm_uret_msrs_list[KVM_MAX_NR_USER_RETURN_MSRS];
>  static struct kvm_user_return_msrs __percpu *user_return_msrs;
>  
>  #define KVM_SUPPORTED_XCR0     (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
> @@ -330,10 +327,10 @@ static void kvm_on_user_return(struct user_return_notifier *urn)
>  		user_return_notifier_unregister(urn);
>  	}
>  	local_irq_restore(flags);
> -	for (slot = 0; slot < user_return_msrs_global.nr; ++slot) {
> +	for (slot = 0; slot < kvm_nr_uret_msrs; ++slot) {
>  		values = &msrs->values[slot];
>  		if (values->host != values->curr) {
> -			wrmsrl(user_return_msrs_global.msrs[slot], values->host);
> +			wrmsrl(kvm_uret_msrs_list[slot], values->host);
>  			values->curr = values->host;
>  		}
>  	}
> @@ -358,9 +355,9 @@ EXPORT_SYMBOL_GPL(kvm_probe_user_return_msr);
>  void kvm_define_user_return_msr(unsigned slot, u32 msr)
>  {
>  	BUG_ON(slot >= KVM_MAX_NR_USER_RETURN_MSRS);
> -	user_return_msrs_global.msrs[slot] = msr;
> -	if (slot >= user_return_msrs_global.nr)
> -		user_return_msrs_global.nr = slot + 1;
> +	kvm_uret_msrs_list[slot] = msr;
> +	if (slot >= kvm_nr_uret_msrs)
> +		kvm_nr_uret_msrs = slot + 1;
>  }
>  EXPORT_SYMBOL_GPL(kvm_define_user_return_msr);
>  
> @@ -368,8 +365,8 @@ int kvm_find_user_return_msr(u32 msr)
>  {
>  	int i;
>  
> -	for (i = 0; i < user_return_msrs_global.nr; ++i) {
> -		if (user_return_msrs_global.msrs[i] == msr)
> +	for (i = 0; i < kvm_nr_uret_msrs; ++i) {
> +		if (kvm_uret_msrs_list[i] == msr)
>  			return i;
>  	}
>  	return -1;
> @@ -383,8 +380,8 @@ static void kvm_user_return_msr_cpu_online(void)
>  	u64 value;
>  	int i;
>  
> -	for (i = 0; i < user_return_msrs_global.nr; ++i) {
> -		rdmsrl_safe(user_return_msrs_global.msrs[i], &value);
> +	for (i = 0; i < kvm_nr_uret_msrs; ++i) {
> +		rdmsrl_safe(kvm_uret_msrs_list[i], &value);
>  		msrs->values[i].host = value;
>  		msrs->values[i].curr = value;
>  	}
> @@ -399,7 +396,7 @@ int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask)
>  	value = (value & mask) | (msrs->values[slot].host & ~mask);
>  	if (value == msrs->values[slot].curr)
>  		return 0;
> -	err = wrmsrl_safe(user_return_msrs_global.msrs[slot], value);
> +	err = wrmsrl_safe(kvm_uret_msrs_list[slot], value);
>  	if (err)
>  		return 1;
>  

Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>

Best regards,
	Maxim Levitsky