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

On 24/07/15 10:59, Roger Pau Monné wrote:
El 24/07/15 a les 10.22, Jan Beulich ha escrit:
On 23.07.15 at 19:12, <andrew.cooper3@xxxxxxxxxx> wrote:
I would go with Jan's suggestion and make
XEN_DOMCTL_{get/set}vcpucontext ineligible for use on HVM guests.
Plus, as you said earlier, a new VCPUOP_initialize.
(Adding the Linux maintainers to get their opinion on the interface)

Just to recap and to make sure I got all the points:

  - vCPU initialization from the toolstack (BSP initialization) is going
to be done using XEN_DOMCTL_sethvmcontext.
  - XEN_DOMCTL_{get/set}vcpucontext is going to return EOPNOTSUPP for
HVM guests.
  - A new vcpu_guest_contatext (vcpu_hvm_context?) is going to be
introduced together with a a new VCPUOP_initialize hypercall

The following is a layout proposal for the new vcpu_context:

struct vcpu_hvm_context {
/* 32bit fields of the structure will be used. */
#define _VCPUHVM_MODE_32B              0
#define VCPUHVM_MODE_32B               (1<<_VCPUHVM_MODE_32B)
/* 64bit fields of the structure will be used. */
#define _VCPUHVM_MODE_64B              1
#define VCPUHVM_MODE_64B               (1<<_VCPUHVM_MODE_64B)
#define _VCPUHVM_online                2
#define VCPUHVM_online                 (1<<_VCPUHVM_online )
     uint32_t flags;                         /* VCPUHVM_* flags.   */
     struct cpu_hvm_regs user_regs;          /* CPU registers.     */

To avoid making the 32bit (and optionally 16bit) massive as a side effect of 64bit, can I suggest

uint32_t flags;
union {

Which allows hvm32_regs to be a far smaller structure.

#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
/* Anonymous union includes both 32- and 64-bit names (e.g., ebp/rbp). */
# define __DECL_REG(n64, n32) union {          \
         uint64_t n64;                          \
         uint32_t n32;                          \
/* Non-gcc sources must always use the proper 64-bit name (e.g., rbp). */
#define __DECL_REG(n64, n32) uint64_t n64

#define __DECL_GP_REG(n) __DECL_REG(r##n, e##n)

struct cpu_hvm_regs {
     /* General purpose registers. */

     /* Control registers.         */
     uint64_t cr[8];
     /* Valid on amd64 only.       */
     uint64_t efer;

     /* Debug registers.           */
     uint64_t db[8];

#undef __DECL_GP_REG
#undef __DECL_REG

Of course the APs will be allowed to start in any mode they wish,
regardless of the mode the guest is currently running on.

To start straight in 64bit, you need gdtr and cs as a minimum

With that in mind, room for each of the task registers, and segment selectors.


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