Jason Lowe-Power has submitted this change. (
https://gem5-review.googlesource.com/c/public/gem5/+/10321 )
Change subject: arch-x86: Make LFENCE a serializing instruction
......................................................................
arch-x86: Make LFENCE a serializing instruction
According to the Intel SDM, no instruction following an LFENCE can begin
execution until after the LFENCE has executed. (This is
less strict than an actual serializing instruction, such as CPUID.)
Serializing instructions (per intel SDM Volume 3A Chapter 8.3) ensure
that no future instruction is fetched until after the serializing
instruction is completed.
By contrast, LFENCE (and other memory-ordering instructions) allows
future instructions to have been fetched; it just prohibits them from
being executed.
Change-Id: If89fcb552192326ab69a581f57d71c95cf5d90e7
Signed-off-by: Isaac Richter <[email protected]>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/10321
Reviewed-by: Jason Lowe-Power <[email protected]>
Maintainer: Jason Lowe-Power <[email protected]>
Tested-by: kokoro <[email protected]>
---
M src/arch/x86/isa/decoder/two_byte_opcodes.isa
1 file changed, 2 insertions(+), 1 deletion(-)
Approvals:
Jason Lowe-Power: Looks good to me, approved; Looks good to me, approved
kokoro: Regressions pass
diff --git a/src/arch/x86/isa/decoder/two_byte_opcodes.isa
b/src/arch/x86/isa/decoder/two_byte_opcodes.isa
index dfb748e..1e09243 100644
--- a/src/arch/x86/isa/decoder/two_byte_opcodes.isa
+++ b/src/arch/x86/isa/decoder/two_byte_opcodes.isa
@@ -785,7 +785,8 @@
0x6: decode MODRM_MOD {
0x3: decode MODRM_REG {
0x5: BasicOperate::LFENCE(
- {{/*Nothing*/}}, IsReadBarrier);
+ {{/*Nothing*/}}, IsReadBarrier,
+ IsSerializeAfter);
0x6: BasicOperate::MFENCE(
{{/*Nothing*/}}, IsMemBarrier);
0x7: BasicOperate::SFENCE(
--
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Gerrit-Project: public/gem5
Gerrit-Branch: master
Gerrit-Change-Id: If89fcb552192326ab69a581f57d71c95cf5d90e7
Gerrit-Change-Number: 10321
Gerrit-PatchSet: 5
Gerrit-Owner: Isaac Richter <[email protected]>
Gerrit-Reviewer: Anthony Gutierrez <[email protected]>
Gerrit-Reviewer: Brandon Potter <[email protected]>
Gerrit-Reviewer: Gabe Black <[email protected]>
Gerrit-Reviewer: Isaac Richter <[email protected]>
Gerrit-Reviewer: Jason Lowe-Power <[email protected]>
Gerrit-Reviewer: kokoro <[email protected]>
Gerrit-CC: Andrea Mondelli <[email protected]>
Gerrit-MessageType: merged
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