[PATCH] kvm: userspace interface

web site: http://kvm.sourceforge.net

mailing list: kvm-devel@lists.sourceforge.net
  (http://lists.sourceforge.net/lists/listinfo/kvm-devel)

The following patchset adds a driver for Intel's hardware virtualization
extensions to the x86 architecture.  The driver adds a character device
(/dev/kvm) that exposes the virtualization capabilities to userspace.  Using
this driver, a process can run a virtual machine (a "guest") in a fully
virtualized PC containing its own virtual hard disks, network adapters, and
display.

Using this driver, one can start multiple virtual machines on a host.

Each virtual machine is a process on the host; a virtual cpu is a thread in
that process.  kill(1), nice(1), top(1) work as expected.  In effect, the
driver adds a third execution mode to the existing two: we now have kernel
mode, user mode, and guest mode.  Guest mode has its own address space mapping
guest physical memory (which is accessible to user mode by mmap()ing
/dev/kvm).  Guest mode has no access to any I/O devices; any such access is
intercepted and directed to user mode for emulation.

The driver supports i386 and x86_64 hosts and guests.  All combinations are
allowed except x86_64 guest on i386 host.  For i386 guests and hosts, both pae
and non-pae paging modes are supported.

SMP hosts and UP guests are supported.  At the moment only Intel
hardware is supported, but AMD virtualization support is being worked on.

Performance currently is non-stellar due to the naive implementation of the
mmu virtualization, which throws away most of the shadow page table entries
every context switch.  We plan to address this in two ways:

- cache shadow page tables across tlb flushes
- wait until AMD and Intel release processors with nested page tables

Currently a virtual desktop is responsive but consumes a lot of CPU.  Under
Windows I tried playing pinball and watching a few flash movies; with a recent
CPU one can hardly feel the virtualization.  Linux/X is slower, probably due
to X being in a separate process.

In addition to the driver, you need a slightly modified qemu to provide I/O
device emulation and the BIOS.

Caveats (akpm: might no longer be true):

- The Windows install currently bluescreens due to a problem with the
  virtual APIC.  We are working on a fix.  A temporary workaround is to
  use an existing image or install through qemu
- Windows 64-bit does not work.  That's also true for qemu, so it's
  probably a problem with the device model.

[bero@arklinux.org: build fix]
[simon.kagstrom@bth.se: build fix, other fixes]
[uril@qumranet.com: KVM: Expose interrupt bitmap]
[akpm@osdl.org: i386 build fix]
[mingo@elte.hu: i386 fixes]
[rdreier@cisco.com: add log levels to all printks]
[randy.dunlap@oracle.com: Fix sparse NULL and C99 struct init warnings]
[anthony@codemonkey.ws: KVM: AMD SVM: 32-bit host support]
Signed-off-by: Yaniv Kamay <yaniv@qumranet.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
Cc: Simon Kagstrom <simon.kagstrom@bth.se>
Cc: Bernhard Rosenkraenzer <bero@arklinux.org>
Signed-off-by: Uri Lublin <uril@qumranet.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Anthony Liguori <anthony@codemonkey.ws>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 397 insertions, 0 deletions

diff --git a/drivers/kvm/paging_tmpl.h b/drivers/kvm/paging_tmpl.h
new file mode 100644
index 00000000000..765c2e1a048
--- /dev/null
+++ b/drivers/kvm/paging_tmpl.h
@@ -0,0 +1,397 @@
+/*
+ * Kernel-based Virtual Machine driver for Linux
+ *
+ * This module enables machines with Intel VT-x extensions to run virtual
+ * machines without emulation or binary translation.
+ *
+ * MMU support
+ *
+ * Copyright (C) 2006 Qumranet, Inc.
+ *
+ * Authors:
+ *   Yaniv Kamay  <yaniv@qumranet.com>
+ *   Avi Kivity   <avi@qumranet.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+/*
+ * We need the mmu code to access both 32-bit and 64-bit guest ptes,
+ * so the code in this file is compiled twice, once per pte size.
+ */
+
+#if PTTYPE == 64
+	#define pt_element_t u64
+	#define guest_walker guest_walker64
+	#define FNAME(name) paging##64_##name
+	#define PT_BASE_ADDR_MASK PT64_BASE_ADDR_MASK
+	#define PT_DIR_BASE_ADDR_MASK PT64_DIR_BASE_ADDR_MASK
+	#define PT_INDEX(addr, level) PT64_INDEX(addr, level)
+	#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
+	#define PT_LEVEL_MASK(level) PT64_LEVEL_MASK(level)
+	#define PT_PTE_COPY_MASK PT64_PTE_COPY_MASK
+	#define PT_NON_PTE_COPY_MASK PT64_NON_PTE_COPY_MASK
+#elif PTTYPE == 32
+	#define pt_element_t u32
+	#define guest_walker guest_walker32
+	#define FNAME(name) paging##32_##name
+	#define PT_BASE_ADDR_MASK PT32_BASE_ADDR_MASK
+	#define PT_DIR_BASE_ADDR_MASK PT32_DIR_BASE_ADDR_MASK
+	#define PT_INDEX(addr, level) PT32_INDEX(addr, level)
+	#define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
+	#define PT_LEVEL_MASK(level) PT32_LEVEL_MASK(level)
+	#define PT_PTE_COPY_MASK PT32_PTE_COPY_MASK
+	#define PT_NON_PTE_COPY_MASK PT32_NON_PTE_COPY_MASK
+#else
+	#error Invalid PTTYPE value
+#endif
+
+/*
+ * The guest_walker structure emulates the behavior of the hardware page
+ * table walker.
+ */
+struct guest_walker {
+	int level;
+	pt_element_t *table;
+	pt_element_t inherited_ar;
+};
+
+static void FNAME(init_walker)(struct guest_walker *walker,
+			       struct kvm_vcpu *vcpu)
+{
+	hpa_t hpa;
+	struct kvm_memory_slot *slot;
+
+	walker->level = vcpu->mmu.root_level;
+	slot = gfn_to_memslot(vcpu->kvm,
+			      (vcpu->cr3 & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT);
+	hpa = safe_gpa_to_hpa(vcpu, vcpu->cr3 & PT64_BASE_ADDR_MASK);
+	walker->table = kmap_atomic(pfn_to_page(hpa >> PAGE_SHIFT), KM_USER0);
+
+	ASSERT((!kvm_arch_ops->is_long_mode(vcpu) && is_pae(vcpu)) ||
+	       (vcpu->cr3 & ~(PAGE_MASK | CR3_FLAGS_MASK)) == 0);
+
+	walker->table = (pt_element_t *)( (unsigned long)walker->table |
+		(unsigned long)(vcpu->cr3 & ~(PAGE_MASK | CR3_FLAGS_MASK)) );
+	walker->inherited_ar = PT_USER_MASK | PT_WRITABLE_MASK;
+}
+
+static void FNAME(release_walker)(struct guest_walker *walker)
+{
+	kunmap_atomic(walker->table, KM_USER0);
+}
+
+static void FNAME(set_pte)(struct kvm_vcpu *vcpu, u64 guest_pte,
+			   u64 *shadow_pte, u64 access_bits)
+{
+	ASSERT(*shadow_pte == 0);
+	access_bits &= guest_pte;
+	*shadow_pte = (guest_pte & PT_PTE_COPY_MASK);
+	set_pte_common(vcpu, shadow_pte, guest_pte & PT_BASE_ADDR_MASK,
+		       guest_pte & PT_DIRTY_MASK, access_bits);
+}
+
+static void FNAME(set_pde)(struct kvm_vcpu *vcpu, u64 guest_pde,
+			   u64 *shadow_pte, u64 access_bits,
+			   int index)
+{
+	gpa_t gaddr;
+
+	ASSERT(*shadow_pte == 0);
+	access_bits &= guest_pde;
+	gaddr = (guest_pde & PT_DIR_BASE_ADDR_MASK) + PAGE_SIZE * index;
+	if (PTTYPE == 32 && is_cpuid_PSE36())
+		gaddr |= (guest_pde & PT32_DIR_PSE36_MASK) <<
+			(32 - PT32_DIR_PSE36_SHIFT);
+	*shadow_pte = (guest_pde & (PT_NON_PTE_COPY_MASK | PT_GLOBAL_MASK)) |
+		          ((guest_pde & PT_DIR_PAT_MASK) >>
+			            (PT_DIR_PAT_SHIFT - PT_PAT_SHIFT));
+	set_pte_common(vcpu, shadow_pte, gaddr,
+		       guest_pde & PT_DIRTY_MASK, access_bits);
+}
+
+/*
+ * Fetch a guest pte from a specific level in the paging hierarchy.
+ */
+static pt_element_t *FNAME(fetch_guest)(struct kvm_vcpu *vcpu,
+					struct guest_walker *walker,
+					int level,
+					gva_t addr)
+{
+
+	ASSERT(level > 0  && level <= walker->level);
+
+	for (;;) {
+		int index = PT_INDEX(addr, walker->level);
+		hpa_t paddr;
+
+		ASSERT(((unsigned long)walker->table & PAGE_MASK) ==
+		       ((unsigned long)&walker->table[index] & PAGE_MASK));
+		if (level == walker->level ||
+		    !is_present_pte(walker->table[index]) ||
+		    (walker->level == PT_DIRECTORY_LEVEL &&
+		     (walker->table[index] & PT_PAGE_SIZE_MASK) &&
+		     (PTTYPE == 64 || is_pse(vcpu))))
+			return &walker->table[index];
+		if (walker->level != 3 || kvm_arch_ops->is_long_mode(vcpu))
+			walker->inherited_ar &= walker->table[index];
+		paddr = safe_gpa_to_hpa(vcpu, walker->table[index] & PT_BASE_ADDR_MASK);
+		kunmap_atomic(walker->table, KM_USER0);
+		walker->table = kmap_atomic(pfn_to_page(paddr >> PAGE_SHIFT),
+					    KM_USER0);
+		--walker->level;
+	}
+}
+
+/*
+ * Fetch a shadow pte for a specific level in the paging hierarchy.
+ */
+static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
+			      struct guest_walker *walker)
+{
+	hpa_t shadow_addr;
+	int level;
+	u64 *prev_shadow_ent = NULL;
+
+	shadow_addr = vcpu->mmu.root_hpa;
+	level = vcpu->mmu.shadow_root_level;
+
+	for (; ; level--) {
+		u32 index = SHADOW_PT_INDEX(addr, level);
+		u64 *shadow_ent = ((u64 *)__va(shadow_addr)) + index;
+		pt_element_t *guest_ent;
+
+		if (is_present_pte(*shadow_ent) || is_io_pte(*shadow_ent)) {
+			if (level == PT_PAGE_TABLE_LEVEL)
+				return shadow_ent;
+			shadow_addr = *shadow_ent & PT64_BASE_ADDR_MASK;
+			prev_shadow_ent = shadow_ent;
+			continue;
+		}
+
+		if (PTTYPE == 32 && level > PT32_ROOT_LEVEL) {
+			ASSERT(level == PT32E_ROOT_LEVEL);
+			guest_ent = FNAME(fetch_guest)(vcpu, walker,
+						       PT32_ROOT_LEVEL, addr);
+		} else
+			guest_ent = FNAME(fetch_guest)(vcpu, walker,
+						       level, addr);
+
+		if (!is_present_pte(*guest_ent))
+			return NULL;
+
+		/* Don't set accessed bit on PAE PDPTRs */
+		if (vcpu->mmu.root_level != 3 || walker->level != 3)
+			*guest_ent |= PT_ACCESSED_MASK;
+
+		if (level == PT_PAGE_TABLE_LEVEL) {
+
+			if (walker->level == PT_DIRECTORY_LEVEL) {
+				if (prev_shadow_ent)
+					*prev_shadow_ent |= PT_SHADOW_PS_MARK;
+				FNAME(set_pde)(vcpu, *guest_ent, shadow_ent,
+					       walker->inherited_ar,
+				          PT_INDEX(addr, PT_PAGE_TABLE_LEVEL));
+			} else {
+				ASSERT(walker->level == PT_PAGE_TABLE_LEVEL);
+				FNAME(set_pte)(vcpu, *guest_ent, shadow_ent, walker->inherited_ar);
+			}
+			return shadow_ent;
+		}
+
+		shadow_addr = kvm_mmu_alloc_page(vcpu, shadow_ent);
+		if (!VALID_PAGE(shadow_addr))
+			return ERR_PTR(-ENOMEM);
+		if (!kvm_arch_ops->is_long_mode(vcpu) && level == 3)
+			*shadow_ent = shadow_addr |
+				(*guest_ent & (PT_PRESENT_MASK | PT_PWT_MASK | PT_PCD_MASK));
+		else {
+			*shadow_ent = shadow_addr |
+				(*guest_ent & PT_NON_PTE_COPY_MASK);
+			*shadow_ent |= (PT_WRITABLE_MASK | PT_USER_MASK);
+		}
+		prev_shadow_ent = shadow_ent;
+	}
+}
+
+/*
+ * The guest faulted for write.  We need to
+ *
+ * - check write permissions
+ * - update the guest pte dirty bit
+ * - update our own dirty page tracking structures
+ */
+static int FNAME(fix_write_pf)(struct kvm_vcpu *vcpu,
+			       u64 *shadow_ent,
+			       struct guest_walker *walker,
+			       gva_t addr,
+			       int user)
+{
+	pt_element_t *guest_ent;
+	int writable_shadow;
+	gfn_t gfn;
+
+	if (is_writeble_pte(*shadow_ent))
+		return 0;
+
+	writable_shadow = *shadow_ent & PT_SHADOW_WRITABLE_MASK;
+	if (user) {
+		/*
+		 * User mode access.  Fail if it's a kernel page or a read-only
+		 * page.
+		 */
+		if (!(*shadow_ent & PT_SHADOW_USER_MASK) || !writable_shadow)
+			return 0;
+		ASSERT(*shadow_ent & PT_USER_MASK);
+	} else
+		/*
+		 * Kernel mode access.  Fail if it's a read-only page and
+		 * supervisor write protection is enabled.
+		 */
+		if (!writable_shadow) {
+			if (is_write_protection(vcpu))
+				return 0;
+			*shadow_ent &= ~PT_USER_MASK;
+		}
+
+	guest_ent = FNAME(fetch_guest)(vcpu, walker, PT_PAGE_TABLE_LEVEL, addr);
+
+	if (!is_present_pte(*guest_ent)) {
+		*shadow_ent = 0;
+		return 0;
+	}
+
+	gfn = (*guest_ent & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
+	mark_page_dirty(vcpu->kvm, gfn);
+	*shadow_ent |= PT_WRITABLE_MASK;
+	*guest_ent |= PT_DIRTY_MASK;
+
+	return 1;
+}
+
+/*
+ * Page fault handler.  There are several causes for a page fault:
+ *   - there is no shadow pte for the guest pte
+ *   - write access through a shadow pte marked read only so that we can set
+ *     the dirty bit
+ *   - write access to a shadow pte marked read only so we can update the page
+ *     dirty bitmap, when userspace requests it
+ *   - mmio access; in this case we will never install a present shadow pte
+ *   - normal guest page fault due to the guest pte marked not present, not
+ *     writable, or not executable
+ *
+ *  Returns: 1 if we need to emulate the instruction, 0 otherwise
+ */
+static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
+			       u32 error_code)
+{
+	int write_fault = error_code & PFERR_WRITE_MASK;
+	int pte_present = error_code & PFERR_PRESENT_MASK;
+	int user_fault = error_code & PFERR_USER_MASK;
+	struct guest_walker walker;
+	u64 *shadow_pte;
+	int fixed;
+
+	/*
+	 * Look up the shadow pte for the faulting address.
+	 */
+	for (;;) {
+		FNAME(init_walker)(&walker, vcpu);
+		shadow_pte = FNAME(fetch)(vcpu, addr, &walker);
+		if (IS_ERR(shadow_pte)) {  /* must be -ENOMEM */
+			nonpaging_flush(vcpu);
+			FNAME(release_walker)(&walker);
+			continue;
+		}
+		break;
+	}
+
+	/*
+	 * The page is not mapped by the guest.  Let the guest handle it.
+	 */
+	if (!shadow_pte) {
+		inject_page_fault(vcpu, addr, error_code);
+		FNAME(release_walker)(&walker);
+		return 0;
+	}
+
+	/*
+	 * Update the shadow pte.
+	 */
+	if (write_fault)
+		fixed = FNAME(fix_write_pf)(vcpu, shadow_pte, &walker, addr,
+					    user_fault);
+	else
+		fixed = fix_read_pf(shadow_pte);
+
+	FNAME(release_walker)(&walker);
+
+	/*
+	 * mmio: emulate if accessible, otherwise its a guest fault.
+	 */
+	if (is_io_pte(*shadow_pte)) {
+		if (may_access(*shadow_pte, write_fault, user_fault))
+			return 1;
+		pgprintk("%s: io work, no access\n", __FUNCTION__);
+		inject_page_fault(vcpu, addr,
+				  error_code | PFERR_PRESENT_MASK);
+		return 0;
+	}
+
+	/*
+	 * pte not present, guest page fault.
+	 */
+	if (pte_present && !fixed) {
+		inject_page_fault(vcpu, addr, error_code);
+		return 0;
+	}
+
+	++kvm_stat.pf_fixed;
+
+	return 0;
+}
+
+static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr)
+{
+	struct guest_walker walker;
+	pt_element_t guest_pte;
+	gpa_t gpa;
+
+	FNAME(init_walker)(&walker, vcpu);
+	guest_pte = *FNAME(fetch_guest)(vcpu, &walker, PT_PAGE_TABLE_LEVEL,
+					vaddr);
+	FNAME(release_walker)(&walker);
+
+	if (!is_present_pte(guest_pte))
+		return UNMAPPED_GVA;
+
+	if (walker.level == PT_DIRECTORY_LEVEL) {
+		ASSERT((guest_pte & PT_PAGE_SIZE_MASK));
+		ASSERT(PTTYPE == 64 || is_pse(vcpu));
+
+		gpa = (guest_pte & PT_DIR_BASE_ADDR_MASK) | (vaddr &
+			(PT_LEVEL_MASK(PT_PAGE_TABLE_LEVEL) | ~PAGE_MASK));
+
+		if (PTTYPE == 32 && is_cpuid_PSE36())
+			gpa |= (guest_pte & PT32_DIR_PSE36_MASK) <<
+					(32 - PT32_DIR_PSE36_SHIFT);
+	} else {
+		gpa = (guest_pte & PT_BASE_ADDR_MASK);
+		gpa |= (vaddr & ~PAGE_MASK);
+	}
+
+	return gpa;
+}
+
+#undef pt_element_t
+#undef guest_walker
+#undef FNAME
+#undef PT_BASE_ADDR_MASK
+#undef PT_INDEX
+#undef SHADOW_PT_INDEX
+#undef PT_LEVEL_MASK
+#undef PT_PTE_COPY_MASK
+#undef PT_NON_PTE_COPY_MASK
+#undef PT_DIR_BASE_ADDR_MASK