Avi Kivity wrote: > On 04/07/2010 11:24 PM, Marcelo Tosatti wrote: >> During initialization, WinXP.32 switches to virtual-8086 mode, with >> paging enabled, to use VGABIOS functions. >> >> Since enter_pmode unconditionally clears IOPL and VM bits in RFLAGS >> >> flags = vmcs_readl(GUEST_RFLAGS); >> flags&= ~(X86_EFLAGS_IOPL | X86_EFLAGS_VM); >> flags |= (vmx->rmode.save_iopl<< IOPL_SHIFT); >> vmcs_writel(GUEST_RFLAGS, flags); >> >> > > > Looks like KVM_SET_REGS should write rmode.save_iopl (and a new save_vm)? Just like we manipulate the flags for guest debugging in the set/get_rflags vendor handlers, the same should happen for IOPL and VM. This is no business of enter_pmode/rmode. > > I think we have a small related bug in realmode emulation - we run the > guest with iopl=3. This means the guest can use pushfl and see the host > iopl instead of the guest iopl. We should run with iopl=0, which causes > pushfl/popfl to #GP, where we can emulate the flags correctly (by > updating rmode.save_iopl and rmode.save_vm). That has lots of > implications however... > > >> And the order of loading state is set_regs (rflags) followed by >> set_sregs (cr0), these bits are lost across save/restore: >> >> savevm 1 >> kvm_arch_save_regs EIP=7a04 cr0=8001003b eflags=33286 >> system_reset >> loadvm 1 >> kvm_arch_save_regs EIP=7a04 cr0=8001003b eflags=10286 >> cont >> kvm: unhandled exit 80000021 >> kvm_run returned -22 >> >> The following patch fixes it, but it has some drawbacks: >> >> - cpu_synchronize_state+writeback is noticeably slow with tpr patching, >> this makes it slower. >> > > Isn't it a very rare event? It has to be - otherwise the decision to go for full sync and individual get/set IOCTL would have been wrong. What happens during tpr patching? > >> - Should be conditional on VMX !unrestricted guest. >> > > Userspace should know nothing of this mess. > >> - Its a fugly workaround. >> > > True. > Still likely the way to go for old kernels. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
