Re: [Xen-devel] [PATCH v4 04/16] xen: Add is_vmware_port_enabled

["Slutz, Donald Christopher" <dslutz@xxxxxxxxxxx>]

On 09/17/14 11:56, Boris Ostrovsky wrote:
>
> On 09/16/2014 08:08 AM, Slutz, Donald Christopher wrote:
>> On 09/12/14 09:08, Boris Ostrovsky wrote:
>>> On 09/11/2014 02:36 PM, Don Slutz wrote:
>>>>    int __get_instruction_length_from_list(struct vcpu *v,
>>>> -        const enum instruction_index *list, unsigned int list_count)
>>>> +                                       const enum instruction_index
>>>> *list,
>>>> +                                       unsigned int list_count,
>>>> +                                       bool_t err_rpt)
>>>>    {
>>>>        struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
>>>>        unsigned int i, j, inst_len = 0;
>>>> @@ -211,10 +222,13 @@ int __get_instruction_length_from_list(struct
>>>> vcpu *v,
>>>>        mismatch: ;
>>>>        }
>>>>    -    gdprintk(XENLOG_WARNING,
>>>> -             "%s: Mismatch between expected and actual instruction
>>>> bytes: "
>>>> -             "eip = %lx\n",  __func__, (unsigned long)vmcb->rip);
>>>> -    hvm_inject_hw_exception(TRAP_gp_fault, 0);
>>>> +    if ( err_rpt )
>>>> +    {
>>>> +        gdprintk(XENLOG_WARNING,
>>>> +                 "%s: Mismatch between expected and actual
>>>> instruction bytes: "
>>>> +                 "eip = %lx\n",  __func__, (unsigned long)vmcb->rip);
>>>> +        hvm_inject_hw_exception(TRAP_gp_fault, 0);
>>>> +    }
>>>>        return 0;
>>>>       done:
>>>> diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
>>>> index b5188e6..9e14d2a 100644
>>>> --- a/xen/arch/x86/hvm/svm/svm.c
>>>> +++ b/xen/arch/x86/hvm/svm/svm.c
>>>> @@ -59,6 +59,7 @@
>>>>    #include <public/sched.h>
>>>>    #include <asm/hvm/vpt.h>
>>>>    #include <asm/hvm/trace.h>
>>>> +#include <asm/hvm/vmport.h>
>>>>    #include <asm/hap.h>
>>>>    #include <asm/apic.h>
>>>>    #include <asm/debugger.h>
>>>> @@ -2065,6 +2066,38 @@ svm_vmexit_do_vmsave(struct vmcb_struct *vmcb,
>>>>        return;
>>>>    }
>>>>    +static void svm_vmexit_gp_intercept(struct cpu_user_regs *regs,
>>>> +                                    struct vcpu *v)
>>>> +{
>>>> +    struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
>>>> +    unsigned long inst_len;
>>>> +    unsigned long inst_addr = svm_rip2pointer(v);
>>>> +    int rc;
>>>> +    static const enum instruction_index list[] = {
>>>> +        INSTR_INL_DX, INSTR_INB_DX, INSTR_OUTL_DX, INSTR_OUTB_DX
>>>> +    };
>>>> +
>>>> +    inst_len = __get_instruction_length_from_list(
>>>> +        v, list, ARRAY_SIZE(list), 0);
>>> I should have asked earlier but I don't think I understand why the
>>> last argument here is 0 (and therefore why you have this last argument
>>> at all).
>>>
>>> Because whether or not you are warning in
>>> __get_instruction_length_from_list() it will still return 0. And that,
>>> in turn, will cause vmport_gp_check() to return an error. And then you
>>> will print another warning in VMPORT_LOG. So there is a warning anyway.
>>>
>> A key part that you appear to have missed is that
>> __get_instruction_length_from_list() uses gdprintk(XENLOG_WARNING,...
>> but VMPORT_DBG_LOG is only available in debug=y builds.  So the new
>> last argument is used to control this.  Since this change includes
>> enabling #GP vmexits, it is now possible for ring 3 users to generate at
>> large volume of these which with gdprintk() can flood the console.
>
> Would it be possible to decide where and whether to print the warning 
> inside __get_instruction_length_from_list() as opposed to passing a 
> new parameter? E.g. if vmware_port_enabled is set and list includes 
> IN/OUT and possibly something else?
>

It could be.  However the test is complex and not something I am willing
to be part of this patch.  So the only thing I have come up with is using
#ifndef NDEBUG around the gdprintk().  This leaves the


         hvm_inject_hw_exception(TRAP_gp_fault, 0);

Which is not correct in this case.  Now are far as I can tell, calling this
twice does the wrong thing for this case.  I.E. turns it into a double 
fault.
For #GP I need to call it with vmcb->exitinfo1 instead of 0.

(Note: v5 posted before I got this.)

I just spent some time checking and found out that even with the cpu
reporting:

(XEN)   - Next-RIP Saved on #VMEXIT

svm_nextrip_insn_length(v) is 0.

(hyper-0-21-54:~>cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 21
model           : 2
model name      : AMD Opteron(tm) Processor 4365 EE
stepping        : 0
microcode       : 0x600081c
...)

Which means to me that by using __get_instruction_length_from_list()
I am reading the instruction bytes 2 times.  Once in
__get_instruction_length_from_list() and once in vmport_gp_check().
This is not too bad since the rate of these is low.  But this does 
suggest to
me that the change to using __get_instruction_length_from_list() was
not the best.  Having a routine that both checks the instruction and
reports on which one was found would be much better.

So do I go with v5, or dropping the use of 
__get_instruction_length_from_list()
in a v6?  (The coding of the new routine will take some time.)

    -Don Slutz


> -boris
>
>>
>>
>>> Second, since this handler appears to be handling #GP only for VMware
>>> guest we should make sure that it is not executed for any other guest.
>>> You do now condition intercept got #GP for such guests only but I
>>> still think having a check here is worth doing. Maybe a BUG() or
>>> ASSERT()?
>>>
>>> The same comments are applicable to VMX code, I suspect.
>>>
>> I will change the check in vmport_gp_check on is_vmware_port_enabled
>> into an ASSERT() so both SVM and VMX will be covered.
>>
>>>> +
>>>> +    rc = vmport_gp_check(regs, v, inst_len, inst_addr,
>>>> +                         vmcb->exitinfo1, vmcb->exitinfo2);
>>>> +    if ( !rc )
>>>> +        __update_guest_eip(regs, inst_len);
>>>> +    else
>>>> +    {
>>>> +        VMPORT_DBG_LOG(VMPORT_LOG_GP_UNKNOWN,
>>>> +                       "gp: rc=%d ei1=0x%lx ei2=0x%lx ip=%"PRIx64
>>>> +                       " (0x%lx,%ld) ax=%"PRIx64" bx=%"PRIx64"
>>>> cx=%"PRIx64
>>>> +                       " dx=%"PRIx64" si=%"PRIx64" di=%"PRIx64, rc,
>>>> +                       (unsigned long)vmcb->exitinfo1,
>>>> +                       (unsigned long)vmcb->exitinfo2, regs->rip,
>>>> inst_addr,
>>>> +                       inst_len, regs->rax, regs->rbx, regs->rcx,
>>>> regs->rdx,
>>>> +                       regs->rsi, regs->rdi);
>>>> +        hvm_inject_hw_exception(TRAP_gp_fault, regs->error_code);
>>>> +    }
>>>> +}
>>>> +
>>> .
>

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