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    Subject[patch 32/33] xen: Place vcpu_info structure into per-cpu memory, if possible
    An experimental patch for Xen allows guests to place their vcpu_info
    structs anywhere. We try to use this to place the vcpu_info into the
    PDA, which allows direct access.

    If this works, then switch to using direct access operations for
    irq_enable, disable, save_fl and restore_fl.

    Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
    Cc: Chris Wright <chrisw@sous-sol.org>
    Cc: Keir Fraser <keir@xensource.com>
    ---
    arch/i386/xen/enlighten.c | 121 +++++++++++++++++++++++++++++++++++++++++-
    arch/i386/xen/setup.c | 8 --
    include/xen/interface/vcpu.h | 13 ++++
    3 files changed, 133 insertions(+), 9 deletions(-)

    ===================================================================
    --- a/arch/i386/xen/enlighten.c
    +++ b/arch/i386/xen/enlighten.c
    @@ -61,9 +61,55 @@ struct start_info *xen_start_info;
    struct start_info *xen_start_info;
    EXPORT_SYMBOL_GPL(xen_start_info);

    +static /* __initdata */ struct shared_info dummy_shared_info;
    +
    +/*
    + * Point at some empty memory to start with. We map the real shared_info
    + * page as soon as fixmap is up and running.
    + */
    +struct shared_info *HYPERVISOR_shared_info = (void *)&dummy_shared_info;
    +
    +/* tristate - -1: not tested, 0: not available, 1: available */
    +static int have_vcpu_info_placement = -1;
    +
    void xen_vcpu_setup(int cpu)
    {
    + struct vcpu_register_vcpu_info info;
    + int err;
    + struct vcpu_info *vcpup;
    +
    per_cpu(xen_vcpu, cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
    +
    + if (!have_vcpu_info_placement)
    + return; /* already tested, not available */
    +
    + vcpup = &per_cpu(xen_vcpu_info, cpu);
    +
    + printk("setting up vcpu for %d: xen_vcpu_info=%p\n",
    + cpu, vcpup);
    +
    + info.mfn = virt_to_mfn(vcpup);
    + info.offset = offset_in_page(vcpup);
    +
    + printk("trying to map vcpu_info %d at %p, mfn %x, offset %d\n",
    + cpu, vcpup, info.mfn, info.offset);
    +
    + /* Check to see if the hypervisor will put the vcpu_info
    + structure where we want it, which allows direct access via
    + a percpu-variable. */
    + err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info);
    +
    + BUG_ON(err != 0 && err != -ENOSYS);
    + BUG_ON(err && have_vcpu_info_placement==1); /* all or nothing */
    +
    + have_vcpu_info_placement = 0;
    +
    + if (err == 0) {
    + have_vcpu_info_placement = 1;
    + per_cpu(xen_vcpu, cpu) = vcpup;
    + printk("cpu %d using vcpu_info at %p\n",
    + cpu, vcpup);
    + }
    }

    static void __init xen_banner(void)
    @@ -123,6 +169,20 @@ static unsigned long xen_save_fl(void)
    return (-flags) & X86_EFLAGS_IF;
    }

    +static unsigned long xen_save_fl_direct(void)
    +{
    + unsigned long flags;
    +
    + /* flag has opposite sense of mask */
    + flags = !x86_read_percpu(xen_vcpu_info.evtchn_upcall_mask);
    +
    + /* convert to IF type flag
    + -0 -> 0x00000000
    + -1 -> 0xffffffff
    + */
    + return (-flags) & X86_EFLAGS_IF;
    +}
    +
    static void xen_restore_fl(unsigned long flags)
    {
    struct vcpu_info *vcpu;
    @@ -149,6 +209,25 @@ static void xen_restore_fl(unsigned long
    }
    }

    +static void xen_restore_fl_direct(unsigned long flags)
    +{
    + /* convert from IF type flag */
    + flags = !(flags & X86_EFLAGS_IF);
    +
    + /* This is an atomic update, so no need to worry about
    + preemption. */
    + x86_write_percpu(xen_vcpu_info.evtchn_upcall_mask, flags);
    +
    + /* If we get preempted here, then any pending event will be
    + handled anyway. */
    +
    + if (flags == 0) {
    + barrier(); /* unmask then check (avoid races) */
    + if (unlikely(x86_read_percpu(xen_vcpu_info.evtchn_upcall_pending)))
    + force_evtchn_callback();
    + }
    +}
    +
    static void xen_irq_disable(void)
    {
    /* There's a one instruction preempt window here. We need to
    @@ -157,6 +236,12 @@ static void xen_irq_disable(void)
    preempt_disable();
    x86_read_percpu(xen_vcpu)->evtchn_upcall_mask = 1;
    preempt_enable_no_resched();
    +}
    +
    +static void xen_irq_disable_direct(void)
    +{
    + /* Atomic update, so preemption not a concern. */
    + x86_write_percpu(xen_vcpu_info.evtchn_upcall_mask, 1);
    }

    static void xen_irq_enable(void)
    @@ -176,6 +261,19 @@ static void xen_irq_enable(void)

    barrier(); /* unmask then check (avoid races) */
    if (unlikely(vcpu->evtchn_upcall_pending))
    + force_evtchn_callback();
    +}
    +
    +static void xen_irq_enable_direct(void)
    +{
    + /* Atomic update, so preemption not a concern. */
    + x86_write_percpu(xen_vcpu_info.evtchn_upcall_mask, 0);
    +
    + /* Doesn't matter if we get preempted here, because any
    + pending event will get dealt with anyway. */
    +
    + barrier(); /* unmask then check (avoid races) */
    + if (unlikely(x86_read_percpu(xen_vcpu_info.evtchn_upcall_pending)))
    force_evtchn_callback();
    }

    @@ -538,9 +636,19 @@ static void xen_flush_tlb_others(const c
    xen_mc_issue(PARAVIRT_LAZY_MMU);
    }

    +static void xen_write_cr2(unsigned long cr2)
    +{
    + x86_read_percpu(xen_vcpu)->arch.cr2 = cr2;
    +}
    +
    static unsigned long xen_read_cr2(void)
    {
    return x86_read_percpu(xen_vcpu)->arch.cr2;
    +}
    +
    +static unsigned long xen_read_cr2_direct(void)
    +{
    + return x86_read_percpu(xen_vcpu_info.arch.cr2);
    }

    static void xen_write_cr4(unsigned long cr4)
    @@ -775,7 +883,7 @@ static const struct paravirt_ops xen_par
    .write_cr0 = native_write_cr0,

    .read_cr2 = xen_read_cr2,
    - .write_cr2 = native_write_cr2,
    + .write_cr2 = xen_write_cr2,

    .read_cr3 = xen_read_cr3,
    .write_cr3 = xen_write_cr3,
    @@ -963,6 +1071,17 @@ static asmlinkage void __init xen_start_
    x86_write_percpu(xen_cr3, __pa(pgd));
    xen_vcpu_setup(0);

    + /* xen_vcpu_setup managed to place the vcpu_info within the
    + pda, so make use of it */
    + BUG_ON(have_vcpu_info_placement == -1);
    + if (have_vcpu_info_placement) {
    + paravirt_ops.save_fl = xen_save_fl_direct;
    + paravirt_ops.restore_fl = xen_restore_fl_direct;
    + paravirt_ops.irq_disable = xen_irq_disable_direct;
    + paravirt_ops.irq_enable = xen_irq_enable_direct;
    + paravirt_ops.read_cr2 = xen_read_cr2_direct;
    + }
    +
    paravirt_ops.kernel_rpl = 1;
    if (xen_feature(XENFEAT_supervisor_mode_kernel))
    paravirt_ops.kernel_rpl = 0;
    ===================================================================
    --- a/arch/i386/xen/setup.c
    +++ b/arch/i386/xen/setup.c
    @@ -22,14 +22,6 @@
    /* These are code, but not functions. Defined in entry.S */
    extern const char xen_hypervisor_callback[];
    extern const char xen_failsafe_callback[];
    -
    -static __initdata struct shared_info init_shared;
    -
    -/*
    - * Point at some empty memory to start with. We map the real shared_info
    - * page as soon as fixmap is up and running.
    - */
    -struct shared_info *HYPERVISOR_shared_info = &init_shared;

    unsigned long *phys_to_machine_mapping;
    EXPORT_SYMBOL(phys_to_machine_mapping);
    ===================================================================
    --- a/include/xen/interface/vcpu.h
    +++ b/include/xen/interface/vcpu.h
    @@ -151,6 +151,19 @@ struct vcpu_set_singleshot_timer {
    #define _VCPU_SSHOTTMR_future (0)
    #define VCPU_SSHOTTMR_future (1U << _VCPU_SSHOTTMR_future)

    +/*
    + * Register a memory location in the guest address space for the
    + * vcpu_info structure. This allows the guest to place the vcpu_info
    + * structure in a convenient place, such as in a per-cpu data area.
    + * The pointer need not be page aligned, but the structure must not
    + * cross a page boundary.
    + */
    +#define VCPUOP_register_vcpu_info 10 /* arg == struct vcpu_info */
    +struct vcpu_register_vcpu_info {
    + uint32_t mfn; /* mfn of page to place vcpu_info */
    + uint32_t offset; /* offset within page */
    +};
    +
    #endif /* __XEN_PUBLIC_VCPU_H__ */

    /*
    --

    -
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