linux-kernel - Re: [PATCH 13/25] KVM: TDX: create/destroy VM structure

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Message-ID: <0e283ec8bfee66c01f49529f924a0a8c43d22657.camel@intel.com>
Date: Wed, 21 Aug 2024 16:52:14 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "tony.lindgren@...ux.intel.com" <tony.lindgren@...ux.intel.com>
CC: "seanjc@...gle.com" <seanjc@...gle.com>, "Huang, Kai"
	<kai.huang@...el.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "nik.borisov@...e.com"
	<nik.borisov@...e.com>, "sean.j.christopherson@...el.com"
	<sean.j.christopherson@...el.com>, "Wang, Wei W" <wei.w.wang@...el.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH 13/25] KVM: TDX: create/destroy VM structure

On Wed, 2024-08-21 at 08:39 +0300, Tony Lindgren wrote:
> > Hmm, we would have to make SEAMCALLs to spin on that lock, where as mutexes
> > can
> > sleep. I suspect that is where it came from. But we are trying to make the
> > code
> > simple and obviously correct and add optimizations later. This might fit
> > that
> > pattern, especially since it is just used during VM creation and teardown.
> 
> For handling the busy retries for SEAMCALL callers, we could just use
> iopoll.h read_poll_timeout(). I think it can handle toggling the resume
> bit while looping, need to test that though. See for example the
> smp_func_do_phymem_cache_wb() for toggling the resume variable.

Nice. It seems worth trying to me.

> 
> The overhead of a SEAMCALL may not be that bad in the retry case.