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    Subject[PATCH] [13/40] i386: Document asm-i386/paravirt.h
    Date

    From: Jeremy Fitzhardinge <jeremy@goop.org>
    Clean things up, and broadly document:
    - the paravirt_ops functions themselves
    - the patching mechanism

    Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
    Signed-off-by: Andi Kleen <ak@suse.de>
    Cc: Rusty Russell <rusty@rustcorp.com.au>

    ---
    include/asm-i386/paravirt.h | 131 ++++++++++++++++++++++++++++++++++++++++----
    1 file changed, 121 insertions(+), 10 deletions(-)

    ===================================================================
    Index: linux/include/asm-i386/paravirt.h
    ===================================================================
    --- linux.orig/include/asm-i386/paravirt.h
    +++ linux/include/asm-i386/paravirt.h
    @@ -21,6 +21,14 @@ struct Xgt_desc_struct;
    struct tss_struct;
    struct mm_struct;
    struct desc_struct;
    +
    +/* Lazy mode for batching updates / context switch */
    +enum paravirt_lazy_mode {
    + PARAVIRT_LAZY_NONE = 0,
    + PARAVIRT_LAZY_MMU = 1,
    + PARAVIRT_LAZY_CPU = 2,
    +};
    +
    struct paravirt_ops
    {
    unsigned int kernel_rpl;
    @@ -37,22 +45,33 @@ struct paravirt_ops
    */
    unsigned (*patch)(u8 type, u16 clobber, void *firstinsn, unsigned len);

    + /* Basic arch-specific setup */
    void (*arch_setup)(void);
    char *(*memory_setup)(void);
    void (*init_IRQ)(void);
    + void (*time_init)(void);

    + /*
    + * Called before/after init_mm pagetable setup. setup_start
    + * may reset %cr3, and may pre-install parts of the pagetable;
    + * pagetable setup is expected to preserve any existing
    + * mapping.
    + */
    void (*pagetable_setup_start)(pgd_t *pgd_base);
    void (*pagetable_setup_done)(pgd_t *pgd_base);

    + /* Print a banner to identify the environment */
    void (*banner)(void);

    + /* Set and set time of day */
    unsigned long (*get_wallclock)(void);
    int (*set_wallclock)(unsigned long);
    - void (*time_init)(void);

    + /* cpuid emulation, mostly so that caps bits can be disabled */
    void (*cpuid)(unsigned int *eax, unsigned int *ebx,
    unsigned int *ecx, unsigned int *edx);

    + /* hooks for various privileged instructions */
    unsigned long (*get_debugreg)(int regno);
    void (*set_debugreg)(int regno, unsigned long value);

    @@ -71,15 +90,23 @@ struct paravirt_ops
    unsigned long (*read_cr4)(void);
    void (*write_cr4)(unsigned long);

    + /*
    + * Get/set interrupt state. save_fl and restore_fl are only
    + * expected to use X86_EFLAGS_IF; all other bits
    + * returned from save_fl are undefined, and may be ignored by
    + * restore_fl.
    + */
    unsigned long (*save_fl)(void);
    void (*restore_fl)(unsigned long);
    void (*irq_disable)(void);
    void (*irq_enable)(void);
    void (*safe_halt)(void);
    void (*halt)(void);
    +
    void (*wbinvd)(void);

    - /* err = 0/-EFAULT. wrmsr returns 0/-EFAULT. */
    + /* MSR, PMC and TSR operations.
    + err = 0/-EFAULT. wrmsr returns 0/-EFAULT. */
    u64 (*read_msr)(unsigned int msr, int *err);
    int (*write_msr)(unsigned int msr, u64 val);

    @@ -88,6 +115,7 @@ struct paravirt_ops
    u64 (*get_scheduled_cycles)(void);
    unsigned long (*get_cpu_khz)(void);

    + /* Segment descriptor handling */
    void (*load_tr_desc)(void);
    void (*load_gdt)(const struct Xgt_desc_struct *);
    void (*load_idt)(const struct Xgt_desc_struct *);
    @@ -105,9 +133,12 @@ struct paravirt_ops
    void (*load_esp0)(struct tss_struct *tss, struct thread_struct *t);

    void (*set_iopl_mask)(unsigned mask);
    -
    void (*io_delay)(void);

    + /*
    + * Hooks for intercepting the creation/use/destruction of an
    + * mm_struct.
    + */
    void (*activate_mm)(struct mm_struct *prev,
    struct mm_struct *next);
    void (*dup_mmap)(struct mm_struct *oldmm,
    @@ -115,30 +146,43 @@ struct paravirt_ops
    void (*exit_mmap)(struct mm_struct *mm);

    #ifdef CONFIG_X86_LOCAL_APIC
    + /*
    + * Direct APIC operations, principally for VMI. Ideally
    + * these shouldn't be in this interface.
    + */
    void (*apic_write)(unsigned long reg, unsigned long v);
    void (*apic_write_atomic)(unsigned long reg, unsigned long v);
    unsigned long (*apic_read)(unsigned long reg);
    void (*setup_boot_clock)(void);
    void (*setup_secondary_clock)(void);
    +
    + void (*startup_ipi_hook)(int phys_apicid,
    + unsigned long start_eip,
    + unsigned long start_esp);
    #endif

    + /* TLB operations */
    void (*flush_tlb_user)(void);
    void (*flush_tlb_kernel)(void);
    void (*flush_tlb_single)(unsigned long addr);

    void (*map_pt_hook)(int type, pte_t *va, u32 pfn);

    + /* Hooks for allocating/releasing pagetable pages */
    void (*alloc_pt)(u32 pfn);
    void (*alloc_pd)(u32 pfn);
    void (*alloc_pd_clone)(u32 pfn, u32 clonepfn, u32 start, u32 count);
    void (*release_pt)(u32 pfn);
    void (*release_pd)(u32 pfn);

    + /* Pagetable manipulation functions */
    void (*set_pte)(pte_t *ptep, pte_t pteval);
    - void (*set_pte_at)(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t pteval);
    + void (*set_pte_at)(struct mm_struct *mm, unsigned long addr,
    + pte_t *ptep, pte_t pteval);
    void (*set_pmd)(pmd_t *pmdp, pmd_t pmdval);
    void (*pte_update)(struct mm_struct *mm, unsigned long addr, pte_t *ptep);
    - void (*pte_update_defer)(struct mm_struct *mm, unsigned long addr, pte_t *ptep);
    + void (*pte_update_defer)(struct mm_struct *mm,
    + unsigned long addr, pte_t *ptep);

    pte_t (*ptep_get_and_clear)(pte_t *ptep);

    @@ -164,13 +208,12 @@ struct paravirt_ops
    pgd_t (*make_pgd)(unsigned long pgd);
    #endif

    - void (*set_lazy_mode)(int mode);
    + /* Set deferred update mode, used for batching operations. */
    + void (*set_lazy_mode)(enum paravirt_lazy_mode mode);

    /* These two are jmp to, not actually called. */
    void (*irq_enable_sysexit)(void);
    void (*iret)(void);
    -
    - void (*startup_ipi_hook)(int phys_apicid, unsigned long start_eip, unsigned long start_esp);
    };

    /* Mark a paravirt probe function. */
    @@ -188,8 +231,10 @@ extern struct paravirt_ops paravirt_ops;
    #define paravirt_clobber(clobber) \
    [paravirt_clobber] "i" (clobber)

    -#define PARAVIRT_CALL "call *(paravirt_ops+%c[paravirt_typenum]*4);"
    -
    +/*
    + * Generate some code, and mark it as patchable by the
    + * apply_paravirt() alternate instruction patcher.
    + */
    #define _paravirt_alt(insn_string, type, clobber) \
    "771:\n\t" insn_string "\n" "772:\n" \
    ".pushsection .parainstructions,\"a\"\n" \
    @@ -199,9 +244,74 @@ extern struct paravirt_ops paravirt_ops;
    " .short " clobber "\n" \
    ".popsection\n"

    +/* Generate patchable code, with the default asm parameters. */
    #define paravirt_alt(insn_string) \
    _paravirt_alt(insn_string, "%c[paravirt_typenum]", "%c[paravirt_clobber]")

    +/*
    + * This generates an indirect call based on the operation type number.
    + * The type number, computed in PARAVIRT_PATCH, is derived from the
    + * offset into the paravirt_ops structure, and can therefore be freely
    + * converted back into a structure offset.
    + */
    +#define PARAVIRT_CALL "call *(paravirt_ops+%c[paravirt_typenum]*4);"
    +
    +/*
    + * These macros are intended to wrap calls into a paravirt_ops
    + * operation, so that they can be later identified and patched at
    + * runtime.
    + *
    + * Normally, a call to a pv_op function is a simple indirect call:
    + * (paravirt_ops.operations)(args...).
    + *
    + * Unfortunately, this is a relatively slow operation for modern CPUs,
    + * because it cannot necessarily determine what the destination
    + * address is. In this case, the address is a runtime constant, so at
    + * the very least we can patch the call to e a simple direct call, or
    + * ideally, patch an inline implementation into the callsite. (Direct
    + * calls are essentially free, because the call and return addresses
    + * are completely predictable.)
    + *
    + * These macros rely on the standard gcc "regparm(3)" calling
    + * convention, in which the first three arguments are placed in %eax,
    + * %edx, %ecx (in that order), and the remaining arguments are placed
    + * on the stack. All caller-save registers (eax,edx,ecx) are expected
    + * to be modified (either clobbered or used for return values).
    + *
    + * The call instruction itself is marked by placing its start address
    + * and size into the .parainstructions section, so that
    + * apply_paravirt() in arch/i386/kernel/alternative.c can do the
    + * appropriate patching under the control of the backend paravirt_ops
    + * implementation.
    + *
    + * Unfortunately there's no way to get gcc to generate the args setup
    + * for the call, and then allow the call itself to be generated by an
    + * inline asm. Because of this, we must do the complete arg setup and
    + * return value handling from within these macros. This is fairly
    + * cumbersome.
    + *
    + * There are 5 sets of PVOP_* macros for dealing with 0-4 arguments.
    + * It could be extended to more arguments, but there would be little
    + * to be gained from that. For each number of arguments, there are
    + * the two VCALL and CALL variants for void and non-void functions.
    + *
    + * When there is a return value, the invoker of the macro must specify
    + * the return type. The macro then uses sizeof() on that type to
    + * determine whether its a 32 or 64 bit value, and places the return
    + * in the right register(s) (just %eax for 32-bit, and %edx:%eax for
    + * 64-bit).
    + *
    + * 64-bit arguments are passed as a pair of adjacent 32-bit arguments
    + * in low,high order.
    + *
    + * Small structures are passed and returned in registers. The macro
    + * calling convention can't directly deal with this, so the wrapper
    + * functions must do this.
    + *
    + * These PVOP_* macros are only defined within this header. This
    + * means that all uses must be wrapped in inline functions. This also
    + * makes sure the incoming and outgoing types are always correct.
    + */
    #define PVOP_CALL0(__rettype, __op) \
    ({ \
    __rettype __ret; \
    @@ -1026,6 +1136,7 @@ static inline unsigned long __raw_local_
    [paravirt_sti_type] "i" (PARAVIRT_PATCH(irq_enable)), \
    paravirt_clobber(CLBR_EAX)

    +/* Make sure as little as possible of this mess escapes. */
    #undef PARAVIRT_CALL
    #undef PVOP_VCALL0
    #undef PVOP_CALL0
    -
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