linux-kernel - Re: [RFC PATCH v3 09/11] KVM: Add new members to struct kvm_gfn

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Date:   Thu, 13 Jul 2023 15:10:14 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     isaku.yamahata@...el.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
        erdemaktas@...gle.com, Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Kai Huang <kai.huang@...el.com>,
        Zhi Wang <zhi.wang.linux@...il.com>, chen.bo@...el.com,
        linux-coco@...ts.linux.dev,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Michael Roth <michael.roth@....com>,
        Yuan Yao <yuan.yao@...ux.intel.com>,
        Yu Zhao <yuzhao@...gle.com>
Subject: Re: [RFC PATCH v3 09/11] KVM: Add new members to struct kvm_gfn_range
 to operate on

+Yu

On Wed, Jun 28, 2023, isaku.yamahata@...el.com wrote:
>  void kvm_mmu_init_memslot_memory_attributes(struct kvm *kvm,
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 1a47cedae8a1..5ca0c8ee4292 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -260,7 +260,13 @@ struct kvm_gfn_range {
>  	struct kvm_memory_slot *slot;
>  	gfn_t start;
>  	gfn_t end;
> -	pte_t pte;
> +	union {
> +		unsigned long attributes;
> +		pte_t pte;
> +		unsigned long callback_arg; /* needs a better name */
> +	};

Making the union needs to be done in a separate patch.  And coming back to this
with fresh eyes, I think it makes sense to give the union a name.  I think an
anonymous union is actually worse in the long run, and there aren't _that_ many
instances to update.  E.g. that way a single build-time assertion can capture
all uses, and it makes it more obvious that the usage is poking into a union.

I'll post a patch separately so that it can be picked up for the MGLRU series
(and maybe even merged ahead of both).