linux-kernel - Re: [PATCH v4 2/4] KVM: SVM: Use unsigned integers when dealing with ASIDs

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Date: Thu, 1 Feb 2024 10:27:28 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH v4 2/4] KVM: SVM: Use unsigned integers when dealing with
 ASIDs

On 1/31/24 17:56, Sean Christopherson wrote:
> Convert all local ASID variables and parameters throughout the SEV code
> from signed integers to unsigned integers.  As ASIDs are fundamentally
> unsigned values, and the global min/max variables are appropriately
> unsigned integers, too.
> 
> Functionally, this is a glorified nop as KVM guarantees min_sev_asid is
> non-zero, and no CPU supports -1u as the _only_ asid, i.e. the signed vs.
> unsigned goof won't cause problems in practice.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Just one minor comment below, but either way...

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>   arch/x86/kvm/svm/sev.c | 18 ++++++++++--------
>   arch/x86/kvm/trace.h   | 10 +++++-----
>   2 files changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 7c000088bca6..04c4c14473fd 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -84,9 +84,10 @@ struct enc_region {
>   };
>   
>   /* Called with the sev_bitmap_lock held, or on shutdown  */
> -static int sev_flush_asids(int min_asid, int max_asid)
> +static int sev_flush_asids(unsigned int min_asid, unsigned int max_asid)
>   {
> -	int ret, asid, error = 0;
> +	int ret, error = 0;
> +	unsigned int asid;
>   
>   	/* Check if there are any ASIDs to reclaim before performing a flush */
>   	asid = find_next_bit(sev_reclaim_asid_bitmap, nr_asids, min_asid);
> @@ -116,7 +117,7 @@ static inline bool is_mirroring_enc_context(struct kvm *kvm)
>   }
>   
>   /* Must be called with the sev_bitmap_lock held */
> -static bool __sev_recycle_asids(int min_asid, int max_asid)
> +static bool __sev_recycle_asids(unsigned int min_asid, unsigned int max_asid)
>   {
>   	if (sev_flush_asids(min_asid, max_asid))
>   		return false;
> @@ -143,8 +144,9 @@ static void sev_misc_cg_uncharge(struct kvm_sev_info *sev)
>   
>   static int sev_asid_new(struct kvm_sev_info *sev)
>   {
> -	int asid, min_asid, max_asid, ret;
> +	unsigned int asid, min_asid, max_asid;
>   	bool retry = true;
> +	int ret;
>   
>   	WARN_ON(sev->misc_cg);
>   	sev->misc_cg = get_current_misc_cg();
> @@ -188,7 +190,7 @@ static int sev_asid_new(struct kvm_sev_info *sev)
>   	return ret;
>   }
>   
> -static int sev_get_asid(struct kvm *kvm)
> +static unsigned int sev_get_asid(struct kvm *kvm)
>   {
>   	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>   
> @@ -284,8 +286,8 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
>   
>   static int sev_bind_asid(struct kvm *kvm, unsigned int handle, int *error)
>   {
> +	unsigned int asid = sev_get_asid(kvm);
>   	struct sev_data_activate activate;
> -	int asid = sev_get_asid(kvm);
>   	int ret;
>   
>   	/* activate ASID on the given handle */
> @@ -2312,7 +2314,7 @@ int sev_cpu_init(struct svm_cpu_data *sd)
>    */
>   static void sev_flush_encrypted_page(struct kvm_vcpu *vcpu, void *va)
>   {
> -	int asid = to_kvm_svm(vcpu->kvm)->sev_info.asid;
> +	unsigned int asid = to_kvm_svm(vcpu->kvm)->sev_info.asid;

Since you're touching this, you could switch this to:

	unsigned int asid = sev_get_asid(vcpu->kvm);

>   
>   	/*
>   	 * Note!  The address must be a kernel address, as regular page walk
> @@ -2630,7 +2632,7 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm)
>   void pre_sev_run(struct vcpu_svm *svm, int cpu)
>   {
>   	struct svm_cpu_data *sd = per_cpu_ptr(&svm_data, cpu);
> -	int asid = sev_get_asid(svm->vcpu.kvm);
> +	unsigned int asid = sev_get_asid(svm->vcpu.kvm);
>   
>   	/* Assign the asid allocated with this SEV guest */
>   	svm->asid = asid;
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index 83843379813e..b82e6ed4f024 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -732,13 +732,13 @@ TRACE_EVENT(kvm_nested_intr_vmexit,
>    * Tracepoint for nested #vmexit because of interrupt pending
>    */
>   TRACE_EVENT(kvm_invlpga,
> -	    TP_PROTO(__u64 rip, int asid, u64 address),
> +	    TP_PROTO(__u64 rip, unsigned int asid, u64 address),
>   	    TP_ARGS(rip, asid, address),
>   
>   	TP_STRUCT__entry(
> -		__field(	__u64,	rip	)
> -		__field(	int,	asid	)
> -		__field(	__u64,	address	)
> +		__field(	__u64,		rip	)
> +		__field(	unsigned int,	asid	)
> +		__field(	__u64,		address	)
>   	),
>   
>   	TP_fast_assign(
> @@ -747,7 +747,7 @@ TRACE_EVENT(kvm_invlpga,
>   		__entry->address	=	address;
>   	),
>   
> -	TP_printk("rip: 0x%016llx asid: %d address: 0x%016llx",
> +	TP_printk("rip: 0x%016llx asid: %u address: 0x%016llx",
>   		  __entry->rip, __entry->asid, __entry->address)
>   );
>