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charset="utf-8"; format="flowed" Hi, I think there is an issue in native_irq_return_ldt: UNTRAIN_RET is used and= can clobber %rax which is expected to be the user rax. A simple fix would be to preserve %rax: diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index a4ba162e52c3..f1fe05289d84 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -728,7 +728,11 @@ native_irq_return_ldt: pushq %rdi /* Stash user RDI */ swapgs /* to kernel GS */ SWITCH_TO_KERNEL_CR3 scratch_reg=3D%rdi /* to kernel CR3 */ + + /* UNTRAIN_RET can clobber %rax, so preserve it */ + movq %rax, %rdi UNTRAIN_RET + movq %rdi, %rax =20 movq PER_CPU_VAR(espfix_waddr), %rdi movq %rax, (0*8)(%rdi) /* user RAX */ But I wonder if we really need to use UNTRAIN_RET in native_irq_return_ldt = because I think we reach this point from the kernel after untrain has already be do= ne, and it looks like we don't do ret afterward (the code just fixup the stack = and then iret). Thanks, alex.