linux-kernel - Re: [PATCH v19 011/130] KVM: Add new members to struct kvm_gfn

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Message-ID: <20240313171428.GK935089@ls.amr.corp.intel.com>
Date: Wed, 13 Mar 2024 10:14:28 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 011/130] KVM: Add new members to struct kvm_gfn_range
 to operate on

On Tue, Mar 12, 2024 at 09:33:31PM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> 
> On 2/26/2024 4:25 PM, isaku.yamahata@...el.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > 
> > Add new members to strut kvm_gfn_range to indicate which mapping
> > (private-vs-shared) to operate on.  only_private and only_shared.  Update
> > mmu notifier, set memory attributes ioctl or KVM gmem callback to
> > initialize them.
> > 
> > It was premature for set_memory_attributes ioctl to call
> > kvm_unmap_gfn_range().  Instead, let kvm_arch_ste_memory_attributes()
> "kvm_arch_ste_memory_attributes()" -> "kvm_vm_set_mem_attributes()" ?

Yes, will fix it.

> > handle it and add a new x86 vendor callback to react to memory attribute
> > change.  [1]
> Which new x86 vendor callback?

Now we don't have it. Will drop this sentnse.

> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 7e7fd25b09b3..0520cd8d03cc 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -264,6 +264,8 @@ struct kvm_gfn_range {
> >   	gfn_t start;
> >   	gfn_t end;
> >   	union kvm_mmu_notifier_arg arg;
> > +	bool only_private;
> > +	bool only_shared;
> 
> IMO, an enum will be clearer than the two flags.
> 
>     enum {
>         PROCESS_PRIVATE_AND_SHARED,
>         PROCESS_ONLY_PRIVATE,
>         PROCESS_ONLY_SHARED,
>     };

The code will be ugly like
"if (== PRIVATE || == PRIVATE_AND_SHARED)" or
"if (== SHARED || == PRIVATE_AND_SHARED)"

two boolean (or two flags) is less error-prone.

Thanks,
-- 
Isaku Yamahata <isaku.yamahata@...el.com>