Re: [PATCH] Calculate correct instruction length for data-fault VM exits on VT-x systems

[Anthony Liguori <aliguori@us.ibm.com>]

Please don't submit patches with mailers that attach as binary attachments.

You'll have to resubmit anyway as your copyright line is wrong (unless 
you really did write this code a thousand years ago ;-))

Regards,

Anthony Liguori

Khoa Huynh wrote:
> On VT-x systems, according to Intel VMX specifications,
> the instruction-length information in VMCS on VM exits
> is not always valid.  The instruction-length field in
> VMCS is ONLY valid in the follwing cases: when the VM
> exit is caused by the execution of instructions that
> cause the VM exit unconditionally or based on the
> execution-control bitmap, a software exception (INT3
> or INT0), or a task switch.
>
> For VM exits caused by data faults (hardware exceptions),
> the instruction-length field in VMCS is actually undefined.
> In these cases, the hypervisor can derive the correct
> instruction length by fetching bytes based on the guest
> instruction pointer and decoding those bytes.  There is
> already a function to do this in the SVM sub-directory.
> This function should be moved up one level to HVM
> sub-directory, so both VMX and SVM can use it.
>
> It should be noted that VMX only uses this instrlen
> function when the hypervisor needs the instruction-length
> info and that info is undefined in VMCS, e.g., for MMIO
> instructions.  In other cases where the instruction-length
> field is valid in VMCS, the hypervisor continues to get
> that info from VMCS (via vmread operation).
>
> I came across this problem in my effort to get Windows
> NT booting on Xen.
>
> There are TWO patches attached below:
>
> * instrlen1.patch effectively moves the instrlen.c file
>   from xen/arch/x86/hvm/svm sub-directory up one level to
>   xen/arch/x86/hvm sub-directory and makes minor changes
>   to instrlen.c so that it will work at its new location.
>
> * instrlen2.patch makes additional changes to VMX code
>   so the hypervisor can use the instrlen function correctly
>   in all modes in cases where the instruction-length field is
>   undefined and read from VMCS in cases where it is defined.
>
> I must acknowledge that most of the code in the first patch
> (instrlen1.patch) does not come from me since the primary
> prupose of this patch is to move the instrlen.c file from
> one location to another in the tree (it also makes some
> minor changes).  The second patch (instrlen2.patch) is
> more meaty :-)
>
> These two patches should apply cleanly to the latest
> xen-unstable tree (hg tip = 9866).
>
> I have tested these patches successfully on two systems
> using a variety of guest OSes (e.g. WinXP, Win2003 Server).
>
> Signed-off-by: Khoa Huynh <khoa@us.ibm.com>
>
> (See attached file: instrlen1.patch)(See attached file: instrlen2.patch)
>
> Regards,
> Khoa
> _________________________________________
> Khoa Huynh, Ph.D.
> IBM Linux Technology Center
> (512) 838-4903; T/L 678-4903; khoa@us.ibm.com
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>
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