Hi John, Thanks for your explanation. I agree with your analysis. I think you can submit your next version patch.
Thanks, Eric > -----Original Message----- > From: Lofgren, John E > Sent: Saturday, September 7, 2019 3:01 AM > To: Dong, Eric <eric.d...@intel.com>; devel@edk2.groups.io > Cc: Ni, Ray <ray...@intel.com>; Laszlo Ersek (ler...@redhat.com) > <ler...@redhat.com> > Subject: RE: [edk2-devel] [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: Fix > #AC split lock > > Hi Eric, > > 1. you are correct, we need to need to handle 63-32 bits. I attach image which > I think will help explain it better. sidt and sgdt instructions, save 10 > bytes (8 > bytes = base, 2 bytes = limit) of data to memory. In the code, its separating > the > base and limit to their own 64 bit space. Since base is offset by 2 bytes and > 64bit, it can cross a cache line causing #ac split lock. We can use two > addition > 16 bit xchg to fix it. We need to use 16bit version since the split of cache > line is > occurring between 63-48 and 47-32. > > 2. no, we don't need to worry about those two xchg because it works with > aligned memory. > > > Thank you, > John > > >-----Original Message----- > >From: Dong, Eric > >Sent: Thursday, September 5, 2019 12:37 AM > >To: devel@edk2.groups.io; Lofgren, John E <john.e.lofg...@intel.com> > >Cc: Ni, Ray <ray...@intel.com>; Laszlo Ersek (ler...@redhat.com) > ><ler...@redhat.com>; Dong, Eric <eric.d...@intel.com> > >Subject: RE: [edk2-devel] [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: > >Fix #AC split lock > > > >Hi John, > > > >I'm not sure whether I understand the code correctly. If not, please > >correct me. > > > >1. You change to the code to only exchange 32 bits(eax) instead of 64 > >bits(rax). After your change, how to handle the above 32 bits value > >(from bit > >32 to bit 63)? > >2. In this file, also have another two xchg codes, do them need to be > >updated also? > > > >Thanks, > >Eric > >> -----Original Message----- > >> From: devel@edk2.groups.io [mailto:devel@edk2.groups.io] On Behalf Of > >> John E Lofgren > >> Sent: Wednesday, September 4, 2019 2:15 AM > >> To: devel@edk2.groups.io > >> Subject: [edk2-devel] [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: Fix > >> #AC split lock > >> > >> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2150 > >> > >> Fix #AC split lock's caused by seperating base and limit from sgdt > >> and sidt by changing xchg operands to 32-bit to stop from crossing > cacheline. > >> > >> Signed-off-by: John E Lofgren <john.e.lofg...@intel.com> > >> --- > >> > >> > >UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nas > >m > >> | 12 ++++++------ > >> 1 file changed, 6 insertions(+), 6 deletions(-) > >> > >> diff --git > >> > >a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.na > >> s > >> m > >> > >b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.na > >> s > >> m > >> index 4db1a09f28..6d83dca4b9 100644 > >> --- > >> > >a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.na > >> s > >> m > >> +++ > >b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm. > >> +++ nasm > >> @@ -184,17 +184,17 @@ HasErrorCode: > >> push rax > >> push rax > >> sidt [rsp] > >> - xchg rax, [rsp + 2] > >> - xchg rax, [rsp] > >> - xchg rax, [rsp + 8] > >> + xchg eax, [rsp + 2] > >> + xchg eax, [rsp] > >> + xchg eax, [rsp + 8] > >> > >> xor rax, rax > >> push rax > >> push rax > >> sgdt [rsp] > >> - xchg rax, [rsp + 2] > >> - xchg rax, [rsp] > >> - xchg rax, [rsp + 8] > >> + xchg eax, [rsp + 2] > >> + xchg eax, [rsp] > >> + xchg eax, [rsp + 8] > >> > >> ;; UINT64 Ldtr, Tr; > >> xor rax, rax > >> -- > >> 2.16.2.windows.1 > >> > >> > >> -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#47007): https://edk2.groups.io/g/devel/message/47007 Mute This Topic: https://groups.io/mt/33129650/21656 Mute #ac: https://groups.io/mk?hashtag=ac&subid=3846945 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
