linux-kernel - Re: [PATCH v8 002/103] Partially revert "KVM: Pass kvm_init()'s opaque param to additional arch funcs"

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Message-ID: <20220825194829.GA2538772@ls.amr.corp.intel.com>
Date:   Thu, 25 Aug 2022 12:48:29 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v8 002/103] Partially revert "KVM: Pass kvm_init()'s
 opaque param to additional arch funcs"

On Thu, Aug 11, 2022 at 09:59:34AM +0000,
"Huang, Kai" <kai.huang@...el.com> wrote:

> On Sun, 2022-08-07 at 15:00 -0700, isaku.yamahata@...el.com wrote:
> > From: Chao Gao <chao.gao@...el.com>
> > 
> > This partially reverts commit b99040853738 ("KVM: Pass kvm_init()'s opaque
> > param to additional arch funcs") remove opaque from
> > kvm_arch_check_processor_compat because no one uses this opaque now.
> > Address conflicts for ARM (due to file movement) and manually handle RISC-V
> > which comes after the commit.  The change about kvm_arch_hardware_setup()
> > in original commit are still needed so they are not reverted.
> > 
> > The current implementation enables hardware (e.g. enable VMX on all CPUs),
> > arch-specific initialization for VM creation, 
> > 
> 
> I guess you need to point out _first_ VM?

Yes. I'll add "first".

> 
> > and disables hardware (in
> > x86, disable VMX on all CPUs) for last VM destruction.
> > 
> > TDX requires its initialization on loading KVM module with VMX enabled on
> > all available CPUs. It needs to enable/disable hardware on module
> > initialization.  To reuse the same logic, one way is to pass around the
> 
> To reuse the same logic for what?  I think you need to be specific (and focus)
> on why we need this patch:  we will opportunistically move CPU compatibility
> check to hardware_enable_nolock(), which doesn't take any argument, and this
> patch is a preparation to do that.
> 
> 
> > unused opaque argument, another way is to remove the unused opaque
> > argument.  This patch is a preparation for the latter by removing the
> > argument
> 
> So how about replacing the last two paragraphs with:
> 
> "
> Initializing TDX will be done during module loading time, and in order to do
> that hardware_enable_all() will be done during module loading time too, as
> initializing TDX requires all cpus being in VMX operation.  As a result, CPU
> compatibility check will be opportunistically moved to hardware_enable_nolock(),
> which doesn't take any argument.  Instead of passing 'opaque' around to
> hardware_enable_nolock() and hardware_enable_all(), just remove the unused
> 'opaque' argument from kvm_arch_check_processor_compat().
> "
> 
> Or even simpler:
> 
> "
> To support TDX, hardware_enable_all() will be done during module loading time. 
> As a result, CPU compatibility check will be opportunistically moved to
> hardware_enable_nolock(), which doesn't take any argument.  Instead of passing
> 'opaque' around to hardware_enable_nolock() and hardware_enable_all(), just
> remove the unused 'opaque' argument from kvm_arch_check_processor_compat().
> "
> 
> With changelog updated:

Thanks, I'll adapt the simpler one.

-- 
Isaku Yamahata <isaku.yamahata@...il.com>