Re: [Xen-devel] [PATCH v6 24/29] xen/x86: allow HVM guests to use hypercalls to bring up vCPUs

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.09.15 at 16:01, <roger.pau@xxxxxxxxxx> wrote:
> Ok thanks, so we seem to have a consensus. Before posting a new 
> revision, does the following vcpu_hvm_context look fine to both of you:
> 
> struct vcpu_hvm_x86_32 {
>     uint32_t eax;
>     uint32_t ecx;
>     uint32_t edx;
>     uint32_t ebx;
>     uint32_t esp;
>     uint32_t ebp;
>     uint32_t esi;
>     uint32_t edi;
>     uint32_t eip;
>     uint32_t eflags;
> 
>     uint32_t cr0;
>     uint32_t cr3;
>     uint32_t cr4;
> 
>     /*
>      * EFER should only be used to set the NXE bit (if required)
>      * when starting a vCPU in 32bit mode with paging enabled.
>      */
>     uint64_t efer;
> 
>     uint32_t cs_base;
>     uint32_t ds_base;
>     uint32_t ss_base;
>     uint32_t es_base;
>     uint32_t tr_base;
>     uint32_t cs_limit;
>     uint32_t ds_limit;
>     uint32_t ss_limit;
>     uint32_t es_limit;
>     uint32_t tr_limit;
>     uint16_t cs_ar;
>     uint16_t ds_ar;
>     uint16_t ss_ar;
>     uint16_t es_ar;
>     uint16_t tr_ar;
> };
> 
> struct vcpu_hvm_x86_64 {
>     uint64_t rax;
>     uint64_t rcx;
>     uint64_t rdx;
>     uint64_t rbx;
>     uint64_t rsp;
>     uint64_t rbp;
>     uint64_t rsi;
>     uint64_t rdi;
>     uint64_t rip;
>     uint64_t rflags;
> 
>     uint64_t cr0;
>     uint64_t cr3;
>     uint64_t cr4;
>     uint64_t efer;
> 
>     /*
>      * Setting the CS attributes field is allowed in order to
>      * start in compatibility mode.
>      */

Hmm, as said before it would seem to me that this would better
(or also) be allowed to work by specifying a suitable 32-bit register
state. Remember that in compatibility mode base and limit matter
again, and I think you also can't start with a nul SS.

>     uint16_t cs_ar;
> };

No tr_* here?

Also, what are the selector values going to be? Do you intend to
pass zero there?

Jan


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