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)?
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?
- Should be conditional on VMX !unrestricted guest.
Userspace should know nothing of this mess.
- Its a fugly workaround.
True.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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