Commit 60223a32 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Jeremy Fitzhardinge
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xen: Place vcpu_info structure into per-cpu memory



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: default avatarJeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Keir Fraser <keir@xensource.com>
parent 3e2b8fbe
......@@ -61,9 +61,63 @@ DEFINE_PER_CPU(unsigned long, xen_cr3);
struct start_info *xen_start_info;
EXPORT_SYMBOL_GPL(xen_start_info);
void xen_vcpu_setup(int cpu)
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;
/*
* Flag to determine whether vcpu info placement is available on all
* VCPUs. We assume it is to start with, and then set it to zero on
* the first failure. This is because it can succeed on some VCPUs
* and not others, since it can involve hypervisor memory allocation,
* or because the guest failed to guarantee all the appropriate
* constraints on all VCPUs (ie buffer can't cross a page boundary).
*
* Note that any particular CPU may be using a placed vcpu structure,
* but we can only optimise if the all are.
*
* 0: not available, 1: available
*/
static int have_vcpu_info_placement = 1;
static void __init 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);
info.mfn = virt_to_mfn(vcpup);
info.offset = offset_in_page(vcpup);
printk(KERN_DEBUG "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);
if (err) {
printk(KERN_DEBUG "register_vcpu_info failed: err=%d\n", err);
have_vcpu_info_placement = 0;
} else {
/* This cpu is using the registered vcpu info, even if
later ones fail to. */
per_cpu(xen_vcpu, cpu) = vcpup;
printk(KERN_DEBUG "cpu %d using vcpu_info at %p\n",
cpu, vcpup);
}
}
static void __init xen_banner(void)
......@@ -123,6 +177,20 @@ 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 +217,25 @@ static void xen_restore_fl(unsigned long flags)
}
}
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
......@@ -159,6 +246,12 @@ static void xen_irq_disable(void)
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)
{
struct vcpu_info *vcpu;
......@@ -179,6 +272,19 @@ static void xen_irq_enable(void)
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();
}
static void xen_safe_halt(void)
{
/* Blocking includes an implicit local_irq_enable(). */
......@@ -551,11 +657,21 @@ static void xen_flush_tlb_others(const cpumask_t *cpus, struct mm_struct *mm,
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)
{
/* never allow TSC to be disabled */
......@@ -753,8 +869,27 @@ static __init void xen_pagetable_setup_done(pgd_t *base)
if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
BUG();
}
}
xen_vcpu_setup(smp_processor_id());
/* This is called once we have the cpu_possible_map */
void __init xen_setup_vcpu_info_placement(void)
{
int cpu;
for_each_possible_cpu(cpu)
xen_vcpu_setup(cpu);
/* xen_vcpu_setup managed to place the vcpu_info within the
percpu area for all cpus, so make use of it */
if (have_vcpu_info_placement) {
printk(KERN_INFO "Xen: using vcpu_info placement\n");
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;
}
}
static const struct paravirt_ops xen_paravirt_ops __initdata = {
......@@ -788,7 +923,7 @@ static const struct paravirt_ops xen_paravirt_ops __initdata = {
.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,
......@@ -974,7 +1109,16 @@ asmlinkage void __init xen_start_kernel(void)
/* keep using Xen gdt for now; no urgent need to change it */
x86_write_percpu(xen_cr3, __pa(pgd));
xen_vcpu_setup(0);
#ifdef CONFIG_SMP
/* Don't do the full vcpu_info placement stuff until we have a
possible map. */
per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];
#else
/* May as well do it now, since there's no good time to call
it later on UP. */
xen_setup_vcpu_info_placement();
#endif
paravirt_ops.kernel_rpl = 1;
if (xen_feature(XENFEAT_supervisor_mode_kernel))
......
......@@ -24,14 +24,6 @@
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);
......
......@@ -142,8 +142,6 @@ void __init xen_smp_prepare_boot_cpu(void)
BUG_ON(smp_processor_id() != 0);
native_smp_prepare_boot_cpu();
xen_vcpu_setup(0);
/* We've switched to the "real" per-cpu gdt, so make sure the
old memory can be recycled */
make_lowmem_page_readwrite(&per_cpu__gdt_page);
......@@ -152,6 +150,8 @@ void __init xen_smp_prepare_boot_cpu(void)
cpus_clear(cpu_sibling_map[cpu]);
cpus_clear(cpu_core_map[cpu]);
}
xen_setup_vcpu_info_placement();
}
void __init xen_smp_prepare_cpus(unsigned int max_cpus)
......@@ -262,7 +262,6 @@ int __cpuinit xen_cpu_up(unsigned int cpu)
init_gdt(cpu);
per_cpu(current_task, cpu) = idle;
xen_vcpu_setup(cpu);
irq_ctx_init(cpu);
xen_setup_timer(cpu);
......
......@@ -38,7 +38,7 @@ static inline unsigned xen_get_lazy_mode(void)
void __init xen_fill_possible_map(void);
void xen_vcpu_setup(int cpu);
void __init xen_setup_vcpu_info_placement(void);
void xen_smp_prepare_boot_cpu(void);
void xen_smp_prepare_cpus(unsigned int max_cpus);
int xen_cpu_up(unsigned int cpu);
......
......@@ -151,4 +151,17 @@ 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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