On 1/18/24 09:46, Gerd Hoffmann wrote:
On Wed, Jan 10, 2024 at 04:43:47PM +0000, West, Catharine wrote:
Disabling cache by default results in violation of BTG protections (if BTG
enabled).
BIOS cannot assume that cache is disabled before it executes as ACM may be required to enable NEM.
Whatever solution needs to be done here cannot evict ACM-enabled NEM.
Well, it's OVMF in a virtual machine. No boot guard involved.
So we could probably go for a OVMF-specific patch here.
But I'd prefer to figure what exactly is happening here before going
down that route. An extreme slowdown just because we flip that bit
doesn't make sense to me.
Why is boot time increasing?
Not clear. It seems to be the lzma uncompress of the firmware volume
in rom / pflash which is very slow. Also it is apparently only
triggered in case pci device assignment is used.
I've seen extreme slowness on physical platforms when we've mixed up the
MTRRs or page tables, causing code to be mapped uncached.
Lzma uncompress of ROM could be pretty slow as well, if the ROM is being
read uncached. Lzma probably reads the data a byte at a time, which is
the worst case for uncached accesses. Since this is a VM, it's not
actually uncached at the hardware level, but I don't know how QEMU/KVM
handles uncached guest mappings.... It may be doing a VMEXIT for every byte.
Anyway, I suggest double-checking your page tables and MTRRs.
--
Brian J. Johnson
Enterprise X86 Lab
Hewlett Packard Enterprise
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#114145): https://edk2.groups.io/g/devel/message/114145
Mute This Topic: https://groups.io/mt/100367559/21656
Group Owner: devel+ow...@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com]
-=-=-=-=-=-=-=-=-=-=-=-
