On 5/24/2022 3:08 PM, Gerd Hoffmann wrote:
On Thu, May 12, 2022 at 11:17:45AM +0800, Xiaoyao Li wrote:
TDX guest cannot go to real mode, so just skip the setup of isa-bios.
Does isa-bios setup cause any actual problems?
(same question for patch #19).
It causes mem_region split and mem_slot deletion on KVM.
TDVF marks pages starting from 0x800000 as TEMP_MEM and TD_HOB, which
are TD's private memory and are TDH_MEM_PAGE_ADD'ed to TD via
KVM_TDX_INIT_MEM_REGION
However, if isa-bios and pc.rom are not skipped, the memory_region
initialization of them is after KVM_TDX_INIT_MEM_REGION in
tdx_machine_done_notify(). (I didn't figure out why this order though)
And the it causes memory region split that splits
[0, ram_below_4g)
to
[0, 0xc0 000),
[0xc0 000, 0xe0 000),
[0xe0 000, 0x100 000),
[0x100 000, ram_below_4g)
which causes mem_slot deletion on KVM. On KVM side, we lose the page
content when mem_slot deletion. Thus, the we lose the content of TD HOB.
Yes, the better solution seems to be ensure KVM_TDX_INIT_MEM_REGION is
called after all the mem region is settled down. But I haven't figured
out the reason why the isa-bios and pc.rom initialization happens after
machine_init_done_notifier
on the other hand, to keep isa-bios and pc.rom, we need additional work
to copy the content from the end_of_4G to end_of_1M.
I'm not sure if isa-bios and pc.rom are needed from people on TD guest,
so I just skip them for simplicity,
"is not needed" IMHO isn't a good enough reason to special-case tdx
here.
take care,
Gerd
