linux-kernel - Re: [PATCH v5 12/22] x86/virt/tdx: Convert all memory regions in memblock to TDX memory

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Date:   Wed, 3 Aug 2022 07:22:51 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     seanjc@...gle.com, pbonzini@...hat.com, len.brown@...el.com,
        tony.luck@...el.com, rafael.j.wysocki@...el.com,
        reinette.chatre@...el.com, dan.j.williams@...el.com,
        peterz@...radead.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        isaku.yamahata@...el.com
Subject: Re: [PATCH v5 12/22] x86/virt/tdx: Convert all memory regions in
 memblock to TDX memory

On 8/2/22 18:30, Kai Huang wrote:
> On Fri, 2022-07-08 at 11:34 +1200, Kai Huang wrote:
>>> Why not just entirely remove the lower 1MB from the memblock structure
>>> on TDX systems?  Do something equivalent to adding this on the kernel
>>> command line:
>>>
>>>  	memmap=1M$0x0
>> I will explore this option.  Thanks!
> Hi Dave,
> 
> After investigating and testing, we cannot simply remove first 1MB from e820
> table which is similar to what 'memmap=1M$0x0' does, as the kernel needs low
> memory as trampoline to bring up all APs.

OK, so don't remove it, but reserve it so that the trampoline code can
use it.