I am running QEMU in TCG mode (my server doesn't have kvm support), and I am getting the memory traces in a x86 guest machine of all memory accesses, including the PCID (process-context identifier, and I need that for my current research), on a linux host. I have seen the TCG PCID feature flag is commented out in target/i386/cpu.c, and if I directly emulate a CPU which has PCID flag I got the warning:
warning: TCG doesn't support requested feature: CPUID.01H:ECX.pcid [bit 17]
so I uncommented the CPUID_EXT_PCID in TCG_EXT_FEATURES, and the CPUID_7_0_EBX_INVPCID in TCG_7_0_EBX_FEATURES, in target/i386/cpu.c. I have seen the PCID in the cr3 register in cpu get set, my question is that I am not sure if there will be any issues with this flag. Why is it commented out by default?
Just in case, I will put my commands here. Here are my configurations for compiling:
./configure --prefix=/tigress/kaifengx/sysroot/ --target-list=x86_64-softmmu,x86_64-linux-user --disable-kvm --disable-vnc --enable-gtk --enable-plugins
And my command for running the QEMU:
qemu-system-x86_64 \
-cpu qemu64,+pcid\
-m 4G \
-icount shift=0 \
-drive if=virtio,file=${DISK},cache=none \
-device pqii \
-trace events=`pwd`/events \
-D ${LOG_FILE} \
-net user,hostfwd=tcp::10022-:22 \
-net nic \
-display none \
-nographic \
-plugin QEMU_PATH/tests/plugin/libtlb.so,arg=inline,arg=io
Best,
Kaifeng