On Wed, May 14, 2008 at 11:30 PM, Daniel Baluta <[EMAIL PROTECTED]> wrote:
> Hello ,
>
> Can you guide me to a deeper understanding of the paravirt ops.
>
> This article
>
> http://lwn.net/Articles/194543/
>
> is pretty short and it dates since August 8, 2006.
>
> Thank-you ,
> Daniel.
>
Starting point is at setup_arch() (arch/x86/kernel/setup_32.c):
#ifdef CONFIG_KVM_CLOCK
kvmclock_init();
#endif
#ifdef CONFIG_VMI
/*
* Must be after max_low_pfn is determined, and before kernel
* pagetables are setup.
*/
vmi_init();
#endif
kvm_guest_init();
>From above we can see the different virtualization technology is being
initialized - VMI and KVM....etc.
Next is arch/x86/kernel/vmi_32.c (API invented by VMWare). One
example structure is this:
static struct {
void (*cpuid)(void /* non-c */);
void (*_set_ldt)(u32 selector);
void (*set_tr)(u32 selector);
void (*write_idt_entry)(struct desc_struct *, int, u32, u32);
void (*write_gdt_entry)(struct desc_struct *, int, u32, u32);
void (*write_ldt_entry)(struct desc_struct *, int, u32, u32);
void (*set_kernel_stack)(u32 selector, u32 sp0);
void (*allocate_page)(u32, u32, u32, u32, u32);
void (*release_page)(u32, u32);
void (*set_pte)(pte_t, pte_t *, unsigned);
void (*update_pte)(pte_t *, unsigned);
void (*set_linear_mapping)(int, void *, u32, u32);
void (*_flush_tlb)(int);
void (*set_initial_ap_state)(int, int);
void (*halt)(void);
void (*set_lazy_mode)(int mode);
} vmi_ops;
And inside this file are like (from activate_vmi()):
para_wrap(pv_cpu_ops.cpuid, vmi_cpuid, cpuid, CPUID);
para_fill(pv_cpu_ops.clts, CLTS);
para_fill(pv_cpu_ops.get_debugreg, GetDR);
para_fill(pv_cpu_ops.set_debugreg, SetDR);
para_fill(pv_cpu_ops.read_cr0, GetCR0);
para_fill(pv_mmu_ops.read_cr2, GetCR2);
para_fill(pv_mmu_ops.read_cr3, GetCR3);
para_fill(pv_cpu_ops.read_cr4, GetCR4);
para_fill(pv_cpu_ops.write_cr0, SetCR0);
para_fill(pv_mmu_ops.write_cr2, SetCR2);
para_fill(pv_mmu_ops.write_cr3, SetCR3);
para_fill(pv_cpu_ops.write_cr4, SetCR4);
para_fill(pv_irq_ops.save_fl, GetInterruptMask);
para_fill(pv_irq_ops.restore_fl, SetInterruptMask);
para_fill(pv_irq_ops.irq_disable, DisableInterrupts
What are these?
Just take a look at include/asm-x86/paravirt.h - which provides the
mapping between the paravirtualized guest OS's resources vs the
actual system resources.
Eg:
struct pv_cpu_ops {
/* hooks for various privileged instructions */
unsigned long (*read_cr0)(void);===> Executing inside the
hypervisor, this is the function actually called, if the guest OS
issued a "read CR0" assembly instruction.
void (*write_cr0)(unsigned long);
unsigned long (*read_cr4_safe)(void);
unsigned long (*read_cr4)(void);
void (*write_cr4)(unsigned long);
void (*load_tr_desc)(void);
void (*load_gdt)(const struct desc_ptr *);
void (*load_idt)(const struct desc_ptr *);
void (*store_gdt)(struct desc_ptr *);
void (*store_idt)(struct desc_ptr *);
void (*set_ldt)(const void *desc, unsigned entries);
unsigned long (*store_tr)(void);
void (*load_tls)(struct thread_struct *t, unsigned int cpu);
void (*write_ldt_entry)(struct desc_struct *ldt, int entrynum,
const void *desc);
The other resources inside paravirt.h is easy to deduce.
Essentially pv_cpu_ops provides the base structure for the different
technologies like KVM/Xen/VMI etc.
--
Regards,
Peter Teoh
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