linux-kernel - Re: [V2 PATCH 0/6] KVM: selftests: selftests for fd-based private memory

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Date:   Wed, 08 Mar 2023 01:59:46 +0000
From:   Ackerley Tng <ackerleytng@...gle.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     vannapurve@...gle.com, seanjc@...gle.com, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, pbonzini@...hat.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        shuah@...nel.org, yang.zhong@...el.com, ricarkol@...gle.com,
        aaronlewis@...gle.com, wei.w.wang@...el.com,
        kirill.shutemov@...ux.intel.com, corbet@....net, hughd@...gle.com,
        jlayton@...nel.org, bfields@...ldses.org,
        akpm@...ux-foundation.org, yu.c.zhang@...ux.intel.com,
        jun.nakajima@...el.com, dave.hansen@...el.com,
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        maciej.szmigiero@...cle.com, mizhang@...gle.com, bgardon@...gle.com
Subject: Re: [V2 PATCH 0/6] KVM: selftests: selftests for fd-based private memory

Chao Peng <chao.p.peng@...ux.intel.com> writes:

>> [...]

>> Chao, I'll work on

>> + Running conversion tests for non-overlapping GPA ranges of
>>    same/different memslots from multiple vcpus
>> + Deleting memslots with restricted memfd while guests are being
>>    executed
>> + Installing multiple memslots with ranges within the same restricted
>>    mem files

>> this week.

> Thanks Ackerley. Looks good to me.

> BTW, for whom may have interest, below are the testcases I added:
> https://github.com/chao-p/linux/commit/24dd1257d5c93acb8c8cc6c76c51cf6869970f8a
> https://github.com/chao-p/linux/commit/39a872ef09d539ce0c953451152eb05276b87018
> https://github.com/chao-p/linux/commit/ddd2c92b268a2fdc6158f82a6169ad1a57f2a01d

> Chao

Hi Chao,

While I was working on the selftests I noticed that this could perhaps
be improved:

https://github.com/chao-p/linux/blob/ddd2c92b268a2fdc6158f82a6169ad1a57f2a01d/virt/kvm/kvm_main.c#L1035

We should use a temporary variable to hold the result of fget(fd).

As it is now, if the user provides any invalide fd, like -1,
slot->restrictedmem.file would be overwritten and lost.

We cannot update slot->restrictedmem.file until after the
file_is_restrictedmem() check.

For now there isn't a big problem because kvm_restrictedmem_bind() is
only called on a new struct kvm_memory_slot, but I think this should be
changed in case the function is used elsewhere in future.

Ackerley