linux-kernel - Re: [PATCH v7 10/20] x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory

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Message-ID: <699700de9d63fa72fda4620d052fda3427193b21.camel@intel.com>
Date:   Thu, 24 Nov 2022 10:02:24 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>
Subject: Re: [PATCH v7 10/20] x86/virt/tdx: Use all system memory when
 initializing TDX module as TDX memory

On Thu, 2022-11-24 at 10:26 +0100, Peter Zijlstra wrote:
> On Wed, Nov 23, 2022 at 05:50:37PM -0800, Dan Williams wrote:
> 
> > arch_add_memory() does not add memory to the page allocator.  For
> > example, memremap_pages() uses arch_add_memory() and explicitly does not
> > release the memory to the page allocator. This check belongs in
> > add_memory_resource() to prevent new memory that violates TDX from being
> > onlined. Hopefully there is also an option to disable TDX from the
> > kernel boot command line to recover memory-hotplug without needing to
> > boot into the BIOS to toggle TDX.
> 
> So I've been pushing for all this to either require: tdx=force on the
> cmdline to boot-time enable, or delay all the memory allocation to the
> first KVM/TDX instance being created.
> 
> That is, by default, none of this crud should ever trigger and consume
> memory if you're not using TDX (most of us really).
> 
> (every machine I have loads kvm.ko unconditionally -- even if I never
> user KVM, so kvm.ko load time is not a valid point in time to do TDX
> enablement).
> 

Thanks for input.  I am fine with 'tdx=force'.

Although, I'd like to point out KVM will have a module parameter 'enable_tdx'.

Hi Dave, Sean, do you have any comments?