Re: [PATCH v2] x86/unaccepted_memory: Do not accept ranges that are no longer E820 RAM

["Gupta, Pankaj" <pankaj.gupta@amd.com>]

>> Accept only whole pages of E820 RAM, and clear the bitmap bits only for the
>> units in which memory was accepted.
> A bit in the bitmap covers the whole unit. If the hole doesn't start and
> end on a unit boundary, the unit at its edge is only partly accepted, but
> its bit gets cleared. The rest of the unit stays unaccepted and nothing
> records it.

Right.

>
> This kernel never touches the hole, but the next one can. memmap= and mem=
> only edit e820_table. kexec_file_load() hands the next kernel
> e820_table_kexec, which is copied before the command line is parsed and
> still has the hole as RAM. The next kernel finds RAM with a clear bit and
> uses it. memmap=1M$0x1fff00000, then kexec into a kernel without it.
>
> On TDX this is new. tdx_accept_memory() works on physical addresses, so
> today the hole is accepted together with the rest of the unit and the
> bitmap stays correct. Only SNP needs the direct mapping.

o.k.

>
> A unit cannot be half accepted. Given that, should we go with what Ard
> suggested and refuse memmap= holes in unaccepted memory instead?

Sure, I will go with Ard's suggestion and drop this patch. I will send 
the series that
refuses memmap= holes in confidential guests instead.

Thanks for looking!
Pankaj