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SubjectRe: [PATCH v12 03/18] xen/pvh: Early bootup changes in PV code (v2).
On 01/01/14 04:35, Konrad Rzeszutek Wilk wrote:
> From: Mukesh Rathor <mukesh.rathor@oracle.com>
>
> In the bootup code for PVH we can trap cpuid via vmexit, so don't
> need to use emulated prefix call. We also check for vector callback
> early on, as it is a required feature. PVH also runs at default kernel
> IOPL.
>
> Finally, pure PV settings are moved to a separate function that are
> only called for pure PV, ie, pv with pvmmu. They are also #ifdef
> with CONFIG_XEN_PVMMU.
[...]
> @@ -331,12 +333,15 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
> break;
> }
>
> - asm(XEN_EMULATE_PREFIX "cpuid"
> - : "=a" (*ax),
> - "=b" (*bx),
> - "=c" (*cx),
> - "=d" (*dx)
> - : "0" (*ax), "2" (*cx));
> + if (xen_pvh_domain())
> + native_cpuid(ax, bx, cx, dx);
> + else
> + asm(XEN_EMULATE_PREFIX "cpuid"
> + : "=a" (*ax),
> + "=b" (*bx),
> + "=c" (*cx),
> + "=d" (*dx)
> + : "0" (*ax), "2" (*cx));

For this one off cpuid call it seems preferrable to me to use the
emulate prefix rather than diverge from PV.

> @@ -1431,13 +1449,18 @@ asmlinkage void __init xen_start_kernel(void)
>
> xen_domain_type = XEN_PV_DOMAIN;
>
> + xen_setup_features();
> + xen_pvh_early_guest_init();
> xen_setup_machphys_mapping();
>
> /* Install Xen paravirt ops */
> pv_info = xen_info;
> pv_init_ops = xen_init_ops;
> - pv_cpu_ops = xen_cpu_ops;
> pv_apic_ops = xen_apic_ops;
> + if (xen_pvh_domain())
> + pv_cpu_ops.cpuid = xen_cpuid;
> + else
> + pv_cpu_ops = xen_cpu_ops;

If cpuid is trapped for PVH guests why does PVH need non-native cpuid op?

David


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