Re: [Xen-devel] [PATCH v3 07/32] xen/x86: fix arch_set_info_guest for HVM guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.07.15 at 18:15, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 23/07/15 17:00, Ian Campbell wrote:
>> On Thu, 2015-07-23 at 17:48 +0200, Roger Pau Monnà wrote:
>>> El 23/07/15 a les 17.32, Jan Beulich ha escrit:
>>>>>>> On 23.07.15 at 17:10, <roger.pau@xxxxxxxxxx> wrote:
>>>>> IMHO introducing a new structure that gets rid of all the PV-only 
>>>>>
>>>>> fields seems like a good option:
>>>>>
>>>>> struct vcpu_hvm_context {
>>>>> #define _VGCF_online                   5
>>>>> #define VGCF_online                    (1<<_VGCF_online)
>>>>>     uint32_t flags;                         /* VGCF_* flags      
>>>>>            
>>>>> */
>>>>>     struct cpu_hvm_user_regs user_regs;     /* User-level CPU 
>>>>> registers     
>>>>> */
>>>>>     /* NB. User pagetable on x86/64 is placed in ctrlreg[1]. */
>>>>>     uint32_t ctrlreg[8];                    /* CR0-CR7 (control 
>>>>> registers)  
>>>>> */
>>>>>     uint32_t debugreg[8];                   /* DB0-DB7 (debug 
>>>>> registers)    
>>>>> */
>>>>> };
>>>>>
>>>>> I'm also seriously considering getting rid of ctrlreg and 
>>>>> debugreg.
>>>>> Since HVM VCPUs will always be started in 32bit flat mode, it 
>>>>> doesn't
>>>>> make sense IMHO to have both the 32 and the 64 version of the 
>>>>> registers, so cpu_hvm_user_regs is always going to be:
>>>>>
>>>>> struct cpu_hvm_user_regs {
>>>>>     uint32_t ebx;
>>>>>     uint32_t ecx;
>>>>>     uint32_t edx;
>>>>>     uint32_t esi;
>>>>>     uint32_t edi;
>>>>>     uint32_t ebp;
>>>>>     uint32_t eax;
>>>>>     uint32_t eip;
>>>>>     uint32_t esp;
>>>>>     uint32_t eflags;
>>>>>     uint16_t cs;
>>>>>     uint16_t ss;
>>>>>     uint16_t es;
>>>>>     uint16_t ds;
>>>>>     uint16_t fs;
>>>>>     uint16_t gs;
>>>>> };
>>>>>
>>>>> We could however do something similar to what's done in ARM and 
>>>>> have
>>>>> a union of both the 32 and the 64bit registers in case we want to
>>>>> start the vCPU in 64bit mode sometime in the future.
>>>> What you gave above is suitable only for VCPUOP_initialise afaict.
>>>> Did you intend this to be the case?
>>> Certainly not, this should also be used by XEN_DOMCTL_setvcpucontext.
>>> I'm afraid I'm missing something obvious, but I don't see why this
>>> couldn't be used by XEN_DOMCTL_setvcpucontext TBH, can you please 
>>> clarify?
>> set/getvcpucontext need to pickle all state for save/restore/migration,
>> not just the start of day state.
> 
> HVM migration doesn't use set/getvcpucontext.
> 
> I would expect an HVMLite-based-PVH to follow suit and just use
> set/gethvmcontext.

Oh, right, but that doesn't mean the respective domctl-s should
produce unconsumable data, or have to guess how to interpret
what gets passed in. I.e. at the very minimum the domctl-s then
should be disallowed for PVH if they can#t be made work right.

Jan

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