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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

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.

Ian.

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