linux-kernel - Re: [PATCH v2 02/29] LoongArch: KVM: Implement kvm module related interface

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Message-ID: <708f97e8-0501-a4d4-2c33-7f4c41339d6b@loongson.cn>
Date:   Tue, 21 Feb 2023 11:02:08 +0800
From:   Tianrui Zhao <zhaotianrui@...ngson.cn>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Mark Brown <broonie@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        Oliver Upton <oliver.upton@...ux.dev>, maobibo@...ngson.cn
Subject: Re: [PATCH v2 02/29] LoongArch: KVM: Implement kvm module related
 interface



在 2023年02月21日 01:46, Paolo Bonzini 写道:
> On 2/20/23 07:57, Tianrui Zhao wrote:
>> +    order = get_order(kvm_vector_size + kvm_enter_guest_size);
>> +    addr = (void *)__get_free_pages(GFP_KERNEL, order);
>> +    if (!addr) {
>> +        free_percpu(vmcs);
>> +        return -ENOMEM;
>> +    }
>> +
>> +    memcpy(addr, kvm_vector_entry, kvm_vector_size);
>> +    memcpy(addr + kvm_vector_size, kvm_enter_guest, 
>> kvm_enter_guest_size);
>> +    flush_icache_range((unsigned long)addr, (unsigned long)addr +
>> +                kvm_vector_size + kvm_enter_guest_size);
>> +
>> +    vpid_mask = read_csr_gstat();
>> +    vpid_mask = (vpid_mask & CSR_GSTAT_GIDBIT) >> 
>> CSR_GSTAT_GIDBIT_SHIFT;
>> +    if (vpid_mask)
>> +        vpid_mask = GENMASK(vpid_mask - 1, 0);
>> +
>> +    for_each_possible_cpu(cpu) {
>> +        context = per_cpu_ptr(vmcs, cpu);
>> +        context->vpid_mask = vpid_mask;
>> +        context->vpid_cache = context->vpid_mask + 1;
>> +        context->last_vcpu = NULL;
>> +        context->kvm_eentry = addr;
>> +        context->kvm_enter_guest = addr + kvm_vector_size;
>> +        context->page_order = order;
>> +    }
>
> A lot of these variables are constant across all pCPUs, any reason to 
> have them in a per-CPU variable?  Likewise, since they are all the 
> same as the constant global vmcs variable, why make them part of 
> struct kvm_context instead of just making them globals?

Ok thanks, it is more appropriate to use global variables to save those 
information.

Thanks
Tianrui Zhao

>
> Also, why does the world switch code need a copy?
>
> Paolo