Thanks much Johnson! We will investigate it based on your comments. > -----Original Message----- > From: Brian J. Johnson <brian.john...@hpe.com> > Sent: Tuesday, January 23, 2024 3:12 AM > To: devel@edk2.groups.io; kra...@redhat.com; West, Catharine > <catharine.w...@intel.com> > Cc: Xu, Min M <min.m...@intel.com>; Ni, Ray <ray...@intel.com>; Wu, > MingliangX <mingliangx...@intel.com>; Yao, Jiewen > <jiewen....@intel.com>; Xue, Shengfeng <xueshengf...@byosoft.com.cn>; > Dong, Eric <eric.d...@intel.com>; Kumar, Rahul R > <rahul.r.ku...@intel.com>; De, Debkumar <debkumar...@intel.com> > Subject: Re: [edk2-devel] [PATCH V1 1/1] UefiCpuPkg/ResetVector: Cache > Disable should not be set by default in CR0 > > 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
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