Hi Tom, Thanks for the comments. I'll add more detailed commits in code to explain why the encryption mask is removed in this patch in next version patch.
Thanks, Dun -----Original Message----- From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Lendacky, Thomas via groups.io Sent: Friday, April 21, 2023 10:54 PM To: Tan, Dun <dun....@intel.com>; devel@edk2.groups.io Cc: Ard Biesheuvel <ardb+tianoc...@kernel.org>; Yao, Jiewen <jiewen....@intel.com>; Justen, Jordan L <jordan.l.jus...@intel.com>; Gerd Hoffmann <kra...@redhat.com>; Ni, Ray <ray...@intel.com> Subject: Re: [edk2-devel] [Patch V3 03/11] OvmfPkg:Remove code that apply AddressEncMask to non-leaf entry On 4/21/23 09:26, Tom Lendacky wrote: > On 4/21/23 03:36, Dun Tan wrote: >> Remove code that apply AddressEncMask to non-leaf entry when split >> smm page table by MemEncryptSevLib. In FvbServicesSmm driver, it >> calls MemEncryptSevClearMmioPageEncMask to clear AddressEncMask bit >> in page table for a specific range. In AMD SEV feature, this >> AddressEncMask bit in page table is used to indicate if the memory is >> guest private memory or shared memory. But all memory used by page >> table are treated as encrypted regardless of encryption bit. >> So remove the EncMask bit for smm non-leaf page table entry doesn't >> impact AMD SEV feature. >> If page split happens in the AddressEncMask bit clear process, there >> will be some new non-leaf entries with AddressEncMask applied in smm >> page table. When ReadyToLock, code in PiSmmCpuDxe module will use >> CpuPageTableLib to modify smm page table. So remove code to apply >> AddressEncMask for new non-leaf entries since CpuPageTableLib doesn't >> consume the EncMask PCD. > > I'm really not a fan of removing the encryption mask, because > technically it is correct to have it present in non-leaf entries. I > really think the pagetable library should be able to work correctly > with or without the encryption mask. Or if we do go this route, there needs to be a really big, informative comment above the areas where the AddressEncMask is now being removed to explain why the code isn't setting the encryption mask (SEV pagetable walk behavior and the fact that the pagetable library is unaware of the encryption bit and encounters errors when trying to walk the entries, etc.). Thanks, Tom > > What would it take to make the pagetable library aware of the mask? > > Thanks, > Tom > >> >> Signed-off-by: Dun Tan <dun....@intel.com> >> Cc: Ard Biesheuvel <ardb+tianoc...@kernel.org> >> Cc: Jiewen Yao <jiewen....@intel.com> >> Cc: Jordan Justen <jordan.l.jus...@intel.com> >> Cc: Gerd Hoffmann <kra...@redhat.com> >> Cc: Tom Lendacky <thomas.lenda...@amd.com> >> Cc: Ray Ni <ray...@intel.com> >> --- >> OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c | 6 >> +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git >> a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c >> b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c >> index a1f6e61c1e..f2b821f6d9 100644 >> --- a/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c >> +++ b/OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeVirtualMemory.c >> @@ -233,7 +233,7 @@ Split2MPageTo4K ( >> // Fill in 2M page entry. >> // >> *PageEntry2M = ((UINT64)(UINTN)PageTableEntry1 | >> - IA32_PG_P | IA32_PG_RW | AddressEncMask); >> + IA32_PG_P | IA32_PG_RW); >> } >> /** >> @@ -352,7 +352,7 @@ SetPageTablePoolReadOnly ( >> PhysicalAddress += LevelSize[Level - 1]; >> } >> - PageTable[Index] = (UINT64)(UINTN)NewPageTable | >> AddressEncMask | >> + PageTable[Index] = (UINT64)(UINTN)NewPageTable | >> IA32_PG_P | IA32_PG_RW; >> PageTable = NewPageTable; >> } >> @@ -440,7 +440,7 @@ Split1GPageTo2M ( >> // Fill in 1G page entry. >> // >> *PageEntry1G = ((UINT64)(UINTN)PageDirectoryEntry | >> - IA32_PG_P | IA32_PG_RW | AddressEncMask); >> + IA32_PG_P | IA32_PG_RW); >> PhysicalAddress2M = PhysicalAddress; >> for (IndexOfPageDirectoryEntries = 0; -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#103456): https://edk2.groups.io/g/devel/message/103456 Mute This Topic: https://groups.io/mt/98406586/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
