linux-kernel - Re: [RFC PATCH 9/9] kvm_main.c: handle atomic memslot update

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Date:   Sun, 18 Sep 2022 18:18:23 +0200
From:   Emanuele Giuseppe Esposito <eesposit@...hat.com>
To:     "Yang, Weijiang" <weijiang.yang@...el.com>, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 9/9] kvm_main.c: handle atomic memslot update



Am 13/09/2022 um 04:30 schrieb Yang, Weijiang:
> 
> On 9/9/2022 6:45 PM, Emanuele Giuseppe Esposito wrote:
>> When kvm_vm_ioctl_set_memory_region_list() is invoked, we need
>> to make sure that all memslots are updated in the inactive list
>> and then swap (preferreably only once) the lists, so that all
>> changes are visible immediately.
> [...]
>> +static int kvm_vm_ioctl_set_memory_region_list(struct kvm *kvm,
>> +               struct kvm_userspace_memory_region_list *list,
>> +               struct kvm_userspace_memory_region_entry __user *mem_arg)
>> +{
>> +    struct kvm_userspace_memory_region_entry *mem, *m_iter;
>> +    struct kvm_userspace_memory_region *mem_region;
>> +    struct kvm_internal_memory_region_list *batch, *b_iter;
>> +    int i, r = 0;
>> +    bool *as_to_swap;
>> +
>> +    /* TODO: limit the number of mem to a max? */
>> +
>> +    if (!list->nent)
>> +        return r;
>> +
>> +    mem = vmemdup_user(mem_arg, array_size(sizeof(*mem), list->nent));
>> +    if (IS_ERR(mem)) {
>> +        r = PTR_ERR(mem);
>> +        goto out;
>> +    }
> 
> IMO, it's more natural to dup the user memory at the first place, i.e.,
> kvm_vm_ioctl,
> 
> it also makes the outlets shorter.
> 

I followed the same pattern as kvm_vcpu_ioctl_set_cpuid2, which performs
the user memory dup inside the call :)

I see your point but I guess it's better to keep all ioctl
implementations similar.

Thank you,
Emanuele