linux-kernel - Re: [PATCH v2 3/3] KVM: SVM: Extend host physical APIC ID field to support more than 8-bit

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Date:   Fri, 3 Dec 2021 10:34:56 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Maxim Levitsky <mlevitsk@...hat.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org
Cc:     pbonzini@...hat.com, joro@...tes.org, seanjc@...gle.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        peterz@...radead.org, hpa@...or.com, jon.grimm@....com
Subject: Re: [PATCH v2 3/3] KVM: SVM: Extend host physical APIC ID field to
 support more than 8-bit

On 12/3/21 1:46 AM, Maxim Levitsky wrote:
> On Thu, 2021-12-02 at 17:58 -0600, Suravee Suthikulpanit wrote:

>> @@ -63,6 +64,7 @@
>>   static DEFINE_HASHTABLE(svm_vm_data_hash, SVM_VM_DATA_HASH_BITS);
>>   static u32 next_vm_id = 0;
>>   static bool next_vm_id_wrapped = 0;
>> +static u64 avic_host_physical_id_mask;
>>   static DEFINE_SPINLOCK(svm_vm_data_hash_lock);
>>   
>>   /*
>> @@ -133,6 +135,20 @@ void avic_vm_destroy(struct kvm *kvm)
>>   	spin_unlock_irqrestore(&svm_vm_data_hash_lock, flags);
>>   }
>>   
>> +static void avic_init_host_physical_apicid_mask(void)
>> +{
>> +	if (!x2apic_mode) {
> Wonder why this is a exported  global variable and not function.
> Not the patch fault though.
>> +		/* If host is in xAPIC mode, default to only 8-bit mask. */
>> +		avic_host_physical_id_mask = 0xffULL;
>> +	} else {
>> +		u32 count = get_count_order(apic_get_max_phys_apicid());
>> +
>> +		avic_host_physical_id_mask = BIT(count) - 1;
> I think that there were some complains about using this macro and instead encouraged
> to use 1 << x directly, but I see it used already in other places in avic.c so I don't know.

And I think it should be BIT_ULL() since avic_host_physical_id_mask is a u64.

Thanks,
Tom

>