C++ xen_mc_issue函数代码示例

static void xen_clts(void)
{
	struct multicall_space mcs;

	mcs = xen_mc_entry(0);

	MULTI_fpu_taskswitch(mcs.mc, 0);

	xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_write_cr0(unsigned long cr0)
{
	struct multicall_space mcs;

	/* Only pay attention to cr0.TS; everything else is
	   ignored. */
	mcs = xen_mc_entry(0);

	MULTI_fpu_taskswitch(mcs.mc, (cr0 & X86_CR0_TS) != 0);

	xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static void xen_write_cr0(unsigned long cr0)
{
	struct multicall_space mcs;

	this_cpu_write(xen_cr0_value, cr0);

	mcs = xen_mc_entry(0);

	MULTI_fpu_taskswitch(mcs.mc, (cr0 & X86_CR0_TS) != 0);

	xen_mc_issue(PARAVIRT_LAZY_CPU);
}

/* Add an MFN override for a particular page */
static int m2p_add_override(unsigned long mfn, struct page *page,
			    struct gnttab_map_grant_ref *kmap_op)
{
	unsigned long flags;
	unsigned long pfn;
	unsigned long uninitialized_var(address);
	unsigned level;
	pte_t *ptep = NULL;

	pfn = page_to_pfn(page);
	if (!PageHighMem(page)) {
		address = (unsigned long)__va(pfn << PAGE_SHIFT);
		ptep = lookup_address(address, &level);
		if (WARN(ptep == NULL || level != PG_LEVEL_4K,
			 "m2p_add_override: pfn %lx not mapped", pfn))
			return -EINVAL;
	}

	if (kmap_op != NULL) {
		if (!PageHighMem(page)) {
			struct multicall_space mcs =
				xen_mc_entry(sizeof(*kmap_op));

			MULTI_grant_table_op(mcs.mc,
					GNTTABOP_map_grant_ref, kmap_op, 1);

			xen_mc_issue(PARAVIRT_LAZY_MMU);
		}
	}
	spin_lock_irqsave(&m2p_override_lock, flags);
	list_add(&page->lru,  &m2p_overrides[mfn_hash(mfn)]);
	spin_unlock_irqrestore(&m2p_override_lock, flags);

	/* p2m(m2p(mfn)) == mfn: the mfn is already present somewhere in
	 * this domain. Set the FOREIGN_FRAME_BIT in the p2m for the other
	 * pfn so that the following mfn_to_pfn(mfn) calls will return the
	 * pfn from the m2p_override (the backend pfn) instead.
	 * We need to do this because the pages shared by the frontend
	 * (xen-blkfront) can be already locked (lock_page, called by
	 * do_read_cache_page); when the userspace backend tries to use them
	 * with direct_IO, mfn_to_pfn returns the pfn of the frontend, so
	 * do_blockdev_direct_IO is going to try to lock the same pages
	 * again resulting in a deadlock.
	 * As a side effect get_user_pages_fast might not be safe on the
	 * frontend pages while they are being shared with the backend,
	 * because mfn_to_pfn (that ends up being called by GUPF) will
	 * return the backend pfn rather than the frontend pfn. */
	pfn = mfn_to_pfn_no_overrides(mfn);
	if (__pfn_to_mfn(pfn) == mfn)
		set_phys_to_machine(pfn, FOREIGN_FRAME(mfn));

	return 0;
}

static void xen_set_ldt(const void *addr, unsigned entries)
{
	struct mmuext_op *op;
	struct multicall_space mcs = xen_mc_entry(sizeof(*op));

	op = mcs.args;
	op->cmd = MMUEXT_SET_LDT;
	op->arg1.linear_addr = (unsigned long)addr;
	op->arg2.nr_ents = entries;

	MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

	xen_mc_issue(PARAVIRT_LAZY_CPU);
}

void xen_set_pte_at(struct mm_struct *mm, unsigned long addr,
		    pte_t *ptep, pte_t pteval)
{
	if (mm == current->mm || mm == &init_mm) {
		if (xen_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
			struct multicall_space mcs;
			mcs = xen_mc_entry(0);

			MULTI_update_va_mapping(mcs.mc, addr, pteval, 0);
			xen_mc_issue(PARAVIRT_LAZY_MMU);
			return;
		} else
			if (HYPERVISOR_update_va_mapping(addr, pteval, 0) == 0)
				return;
	}
	xen_set_pte(ptep, pteval);
}

void xen_set_pmd(pmd_t *ptr, pmd_t val)
{
	struct multicall_space mcs;
	struct mmu_update *u;

	preempt_disable();

	mcs = xen_mc_entry(sizeof(*u));
	u = mcs.args;
	u->ptr = virt_to_machine(ptr).maddr;
	u->val = pmd_val_ma(val);
	MULTI_mmu_update(mcs.mc, u, 1, NULL, DOMID_SELF);

	xen_mc_issue(PARAVIRT_LAZY_MMU);

	preempt_enable();
}

static void xen_load_tls(struct thread_struct *t, unsigned int cpu)
{
	if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_CPU) {
#ifdef CONFIG_X86_32
		lazy_load_gs(0);
#else
		loadsegment(fs, 0);
#endif
	}

	xen_mc_batch();

	load_TLS_descriptor(t, cpu, 0);
	load_TLS_descriptor(t, cpu, 1);
	load_TLS_descriptor(t, cpu, 2);

	xen_mc_issue(PARAVIRT_LAZY_CPU);
}

/* Release a pagetables pages back as normal RW */
static void xen_pgd_unpin(pgd_t *pgd)
{
	struct mmuext_op *op;
	struct multicall_space mcs;

	xen_mc_batch();

	mcs = __xen_mc_entry(sizeof(*op));

	op = mcs.args;
	op->cmd = MMUEXT_UNPIN_TABLE;
	op->arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(pgd)));

	MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);

	pgd_walk(pgd, unpin_page, TASK_SIZE);

	xen_mc_issue(0);
}

static void xen_load_tls(struct thread_struct *t, unsigned int cpu)
{
	/*
	 * XXX sleazy hack: If we're being called in a lazy-cpu zone
	 * and lazy gs handling is enabled, it means we're in a
	 * context switch, and %gs has just been saved.  This means we
	 * can zero it out to prevent faults on exit from the
	 * hypervisor if the next process has no %gs.  Either way, it
	 * has been saved, and the new value will get loaded properly.
	 * This will go away as soon as Xen has been modified to not
	 * save/restore %gs for normal hypercalls.
	 *
	 * On x86_64, this hack is not used for %gs, because gs points
	 * to KERNEL_GS_BASE (and uses it for PDA references), so we
	 * must not zero %gs on x86_64
	 *
	 * For x86_64, we need to zero %fs, otherwise we may get an
	 * exception between the new %fs descriptor being loaded and
	 * %fs being effectively cleared at __switch_to().
	 */
	if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_CPU) {
#ifdef CONFIG_X86_32
		lazy_load_gs(0);
#else
		loadsegment(fs, 0);
#endif
	}

	xen_mc_batch();

	load_TLS_descriptor(t, cpu, 0);
	load_TLS_descriptor(t, cpu, 1);
	load_TLS_descriptor(t, cpu, 2);

	xen_mc_issue(PARAVIRT_LAZY_CPU);
}

static int m2p_remove_override(struct page *page,
			       struct gnttab_map_grant_ref *kmap_op,
			       unsigned long mfn)
{
	unsigned long flags;
	unsigned long pfn;
	unsigned long uninitialized_var(address);
	unsigned level;
	pte_t *ptep = NULL;

	pfn = page_to_pfn(page);

	if (!PageHighMem(page)) {
		address = (unsigned long)__va(pfn << PAGE_SHIFT);
		ptep = lookup_address(address, &level);

		if (WARN(ptep == NULL || level != PG_LEVEL_4K,
			 "m2p_remove_override: pfn %lx not mapped", pfn))
			return -EINVAL;
	}

	spin_lock_irqsave(&m2p_override_lock, flags);
	list_del(&page->lru);
	spin_unlock_irqrestore(&m2p_override_lock, flags);

	if (kmap_op != NULL) {
		if (!PageHighMem(page)) {
			struct multicall_space mcs;
			struct gnttab_unmap_and_replace *unmap_op;
			struct page *scratch_page = get_balloon_scratch_page();
			unsigned long scratch_page_address = (unsigned long)
				__va(page_to_pfn(scratch_page) << PAGE_SHIFT);

			/*
			 * It might be that we queued all the m2p grant table
			 * hypercalls in a multicall, then m2p_remove_override
			 * get called before the multicall has actually been
			 * issued. In this case handle is going to -1 because
			 * it hasn't been modified yet.
			 */
			if (kmap_op->handle == -1)
				xen_mc_flush();
			/*
			 * Now if kmap_op->handle is negative it means that the
			 * hypercall actually returned an error.
			 */
			if (kmap_op->handle == GNTST_general_error) {
				pr_warn("m2p_remove_override: pfn %lx mfn %lx, failed to modify kernel mappings",
					pfn, mfn);
				put_balloon_scratch_page();
				return -1;
			}

			xen_mc_batch();

			mcs = __xen_mc_entry(
				sizeof(struct gnttab_unmap_and_replace));
			unmap_op = mcs.args;
			unmap_op->host_addr = kmap_op->host_addr;
			unmap_op->new_addr = scratch_page_address;
			unmap_op->handle = kmap_op->handle;

			MULTI_grant_table_op(mcs.mc,
				GNTTABOP_unmap_and_replace, unmap_op, 1);

			mcs = __xen_mc_entry(0);
			MULTI_update_va_mapping(mcs.mc, scratch_page_address,
					pfn_pte(page_to_pfn(scratch_page),
					PAGE_KERNEL_RO), 0);

			xen_mc_issue(PARAVIRT_LAZY_MMU);

			kmap_op->host_addr = 0;
			put_balloon_scratch_page();
		}
	}

	/* p2m(m2p(mfn)) == FOREIGN_FRAME(mfn): the mfn is already present
	 * somewhere in this domain, even before being added to the
	 * m2p_override (see comment above in m2p_add_override).
	 * If there are no other entries in the m2p_override corresponding
	 * to this mfn, then remove the FOREIGN_FRAME_BIT from the p2m for
	 * the original pfn (the one shared by the frontend): the backend
	 * cannot do any IO on this page anymore because it has been
	 * unshared. Removing the FOREIGN_FRAME_BIT from the p2m entry of
	 * the original pfn causes mfn_to_pfn(mfn) to return the frontend
	 * pfn again. */
	mfn &= ~FOREIGN_FRAME_BIT;
	pfn = mfn_to_pfn_no_overrides(mfn);
	if (__pfn_to_mfn(pfn) == FOREIGN_FRAME(mfn) &&
			m2p_find_override(mfn) == NULL)
		set_phys_to_machine(pfn, mfn);

	return 0;
}

int m2p_remove_override(struct page *page, bool clear_pte)
{
	unsigned long flags;
	unsigned long mfn;
	unsigned long pfn;
	unsigned long uninitialized_var(address);
	unsigned level;
	pte_t *ptep = NULL;
	int ret = 0;

	pfn = page_to_pfn(page);
	mfn = get_phys_to_machine(pfn);
	if (mfn == INVALID_P2M_ENTRY || !(mfn & FOREIGN_FRAME_BIT))
		return -EINVAL;

	if (!PageHighMem(page)) {
		address = (unsigned long)__va(pfn << PAGE_SHIFT);
		ptep = lookup_address(address, &level);

		if (WARN(ptep == NULL || level != PG_LEVEL_4K,
					"m2p_remove_override: pfn %lx not mapped", pfn))
			return -EINVAL;
	}

	spin_lock_irqsave(&m2p_override_lock, flags);
	list_del(&page->lru);
	spin_unlock_irqrestore(&m2p_override_lock, flags);
	WARN_ON(!PagePrivate(page));
	ClearPagePrivate(page);

	if (clear_pte) {
		struct gnttab_map_grant_ref *map_op =
			(struct gnttab_map_grant_ref *) page->index;
		set_phys_to_machine(pfn, map_op->dev_bus_addr);
		if (!PageHighMem(page)) {
			struct multicall_space mcs;
			struct gnttab_unmap_grant_ref *unmap_op;

			/*
			 * It might be that we queued all the m2p grant table
			 * hypercalls in a multicall, then m2p_remove_override
			 * get called before the multicall has actually been
			 * issued. In this case handle is going to -1 because
			 * it hasn't been modified yet.
			 */
			if (map_op->handle == -1)
				xen_mc_flush();
			/*
			 * Now if map_op->handle is negative it means that the
			 * hypercall actually returned an error.
			 */
			if (map_op->handle == GNTST_general_error) {
				printk(KERN_WARNING "m2p_remove_override: "
						"pfn %lx mfn %lx, failed to modify kernel mappings",
						pfn, mfn);
				return -1;
			}

			mcs = xen_mc_entry(
					sizeof(struct gnttab_unmap_grant_ref));
			unmap_op = mcs.args;
			unmap_op->host_addr = map_op->host_addr;
			unmap_op->handle = map_op->handle;
			unmap_op->dev_bus_addr = 0;

			MULTI_grant_table_op(mcs.mc,
					GNTTABOP_unmap_grant_ref, unmap_op, 1);

			xen_mc_issue(PARAVIRT_LAZY_MMU);

			set_pte_at(&init_mm, address, ptep,
					pfn_pte(pfn, PAGE_KERNEL));
			__flush_tlb_single(address);
			map_op->host_addr = 0;
		}
	} else
		set_phys_to_machine(pfn, page->index);

	/* p2m(m2p(mfn)) == FOREIGN_FRAME(mfn): the mfn is already present
	 * somewhere in this domain, even before being added to the
	 * m2p_override (see comment above in m2p_add_override).
	 * If there are no other entries in the m2p_override corresponding
	 * to this mfn, then remove the FOREIGN_FRAME_BIT from the p2m for
	 * the original pfn (the one shared by the frontend): the backend
	 * cannot do any IO on this page anymore because it has been
	 * unshared. Removing the FOREIGN_FRAME_BIT from the p2m entry of
	 * the original pfn causes mfn_to_pfn(mfn) to return the frontend
	 * pfn again. */
	mfn &= ~FOREIGN_FRAME_BIT;
	ret = __get_user(pfn, &machine_to_phys_mapping[mfn]);
	if (ret == 0 && get_phys_to_machine(pfn) == FOREIGN_FRAME(mfn) &&
			m2p_find_override(mfn) == NULL)
		set_phys_to_machine(pfn, mfn);

	return 0;
}