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cpu-kvm, arch-x86: flush TLB after syscalls (#411)

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Modified the x86 KVM-in-SE syscall handler to flush the TLB following
each syscall, in case the page table has been modified. This is done by
reloading the value in %cr3. Doing this requires an intermediate GPR,
which we store in a new scratch buffer following the syscall code at
address `syscallDataBuf`.

GitHub issue: https://github.com/gem5/gem5/issues/409
This commit is contained in:
Jason Lowe-Power
2023-10-09 08:16:06 -07:00
committed by GitHub
parent 5cd70bf9bf 7a0e84d853
commit d4be9c76c5
1 changed files with 22 additions and 0 deletions
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22
src/arch/x86/process.cc
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@@ -483,13 +483,35 @@ X86_64Process::initState()
physProxy.writeBlob(idtPhysAddr + 0xE0, &PFGate, sizeof(PFGate));
/* System call handler */
// First, we write to the MMIO m5ops range (0xffffc90000007000)
// to trap out of the VM back into gem5 to emulate the system
// call. Upon re-entering the VM, we need to flush the TLB in
// case the system call modified existing page mappings (e.g.,
// munmap, mremap, brk). To do this, we can simply read/write
// cr3; however, doing so requires saving the value to an
// intermediate GPR (%rax, in this case). We save/restore the
// value of %rax in the scratch region syscallDataBuf.
const Addr syscallDataBuf = syscallCodeVirtAddr + 0x100;
uint8_t syscallBlob[] = {
// mov %rax, (0xffffc90000007000)
0x48, 0xa3, 0x00, 0x70, 0x00,
0x00, 0x00, 0xc9, 0xff, 0xff,
// mov %rax, (syscallDataBuf)
0x48, 0xa3, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00,
// mov %cr3, %rax
0x0f, 0x20, 0xd8,
// mov %rax, %cr3
0x0f, 0x22, 0xd8,
// mov (syscallDataBuf), %rax
0x48, 0xa1, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00,
// sysret
0x48, 0x0f, 0x07
};
assert(syscallDataBuf >= syscallCodePhysAddr + sizeof syscallBlob);
std::memcpy(&syscallBlob[12], &syscallDataBuf, sizeof syscallDataBuf);
std::memcpy(&syscallBlob[28], &syscallDataBuf, sizeof syscallDataBuf);
physProxy.writeBlob(syscallCodePhysAddr,
syscallBlob, sizeof(syscallBlob));