xen: Complete pagetable pinning

Xen requires all active pagetables to be marked read-only.  When the
base of the pagetable is loaded into %cr3, the hypervisor validates
the entire pagetable and only allows the load to proceed if it all
checks out.

This is pretty slow, so to mitigate this cost Xen has a notion of
pinned pagetables.  Pinned pagetables are pagetables which are
considered to be active even if no processor's cr3 is pointing to is.
This means that it must remain read-only and all updates are validated
by the hypervisor.  This makes context switches much cheaper, because
the hypervisor doesn't need to revalidate the pagetable each time.

This also adds a new paravirt hook which is called during setup once
the zones and memory allocator have been initialized.  When the
init_mm pagetable is first built, the struct page array does not yet
exist, and so there's nowhere to put he init_mm pagetable's PG_pinned
flags.  Once the zones are initialized and the struct page array
exists, we can set the PG_pinned flags for those pages.

This patch also adds the Xen support for pte pages allocated out of
highmem (highpte) by implementing xen_kmap_atomic_pte.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Zach Amsden <zach@vmware.com>

1 files changed, 170 insertions, 90 deletions

diff --git a/arch/i386/xen/mmu.c b/arch/i386/xen/mmu.c
index de16cb5f55ca..53501ce2d15c 100644
--- a/arch/i386/xen/mmu.c
+++ b/arch/i386/xen/mmu.c
@@ -38,19 +38,22 @@
  *
  * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
  */
+#include <linux/highmem.h>
 #include <linux/bug.h>
 #include <linux/sched.h>
 
 #include <asm/pgtable.h>
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
+#include <asm/paravirt.h>
 
 #include <asm/xen/hypercall.h>
-#include <asm/paravirt.h>
+#include <asm/xen/hypervisor.h>
 
 #include <xen/page.h>
 #include <xen/interface/xen.h>
 
+#include "multicalls.h"
 #include "mmu.h"
 
 xmaddr_t arbitrary_virt_to_machine(unsigned long address)
@@ -92,16 +95,6 @@ void make_lowmem_page_readwrite(void *vaddr)
 }
 
 
-void xen_set_pte(pte_t *ptep, pte_t pte)
-{
-        struct mmu_update u;
-
-        u.ptr = virt_to_machine(ptep).maddr;
-        u.val = pte_val_ma(pte);
-        if (HYPERVISOR_mmu_update(&u, 1, NULL, DOMID_SELF) < 0)
-                BUG();
-}
-
 void xen_set_pmd(pmd_t *ptr, pmd_t val)
 {
         struct mmu_update u;
@@ -112,18 +105,6 @@ void xen_set_pmd(pmd_t *ptr, pmd_t val)
                 BUG();
 }
 
-#ifdef CONFIG_X86_PAE
-void xen_set_pud(pud_t *ptr, pud_t val)
-{
-        struct mmu_update u;
-
-        u.ptr = virt_to_machine(ptr).maddr;
-        u.val = pud_val_ma(val);
-        if (HYPERVISOR_mmu_update(&u, 1, NULL, DOMID_SELF) < 0)
-                BUG();
-}
-#endif
-
 /*
  * Associate a virtual page frame with a given physical page frame
  * and protection flags for that frame.
@@ -170,6 +151,23 @@ void xen_set_pte_at(struct mm_struct *mm, unsigned long addr,
 }
 
 #ifdef CONFIG_X86_PAE
+void xen_set_pud(pud_t *ptr, pud_t val)
+{
+        struct mmu_update u;
+
+        u.ptr = virt_to_machine(ptr).maddr;
+        u.val = pud_val_ma(val);
+        if (HYPERVISOR_mmu_update(&u, 1, NULL, DOMID_SELF) < 0)
+                BUG();
+}
+
+void xen_set_pte(pte_t *ptep, pte_t pte)
+{
+        ptep->pte_high = pte.pte_high;
+        smp_wmb();
+        ptep->pte_low = pte.pte_low;
+}
+
 void xen_set_pte_atomic(pte_t *ptep, pte_t pte)
 {
         set_64bit((u64 *)ptep, pte_val_ma(pte));
@@ -239,6 +237,11 @@ pgd_t xen_make_pgd(unsigned long long pgd)
         return (pgd_t){ pgd };
 }
 #else  /* !PAE */
+void xen_set_pte(pte_t *ptep, pte_t pte)
+{
+        *ptep = pte;
+}
+
 unsigned long xen_pte_val(pte_t pte)
 {
         unsigned long ret = pte.pte_low;
@@ -249,13 +252,6 @@ unsigned long xen_pte_val(pte_t pte)
         return ret;
 }
 
-unsigned long xen_pmd_val(pmd_t pmd)
-{
-        /* a BUG here is a lot easier to track down than a NULL eip */
-        BUG();
-        return 0;
-}
-
 unsigned long xen_pgd_val(pgd_t pgd)
 {
         unsigned long ret = pgd.pgd;
@@ -272,13 +268,6 @@ pte_t xen_make_pte(unsigned long pte)
         return (pte_t){ pte };
 }
 
-pmd_t xen_make_pmd(unsigned long pmd)
-{
-        /* a BUG here is a lot easier to track down than a NULL eip */
-        BUG();
-        return __pmd(0);
-}
-
 pgd_t xen_make_pgd(unsigned long pgd)
 {
         if (pgd & _PAGE_PRESENT)
@@ -290,108 +279,199 @@ pgd_t xen_make_pgd(unsigned long pgd)
 
 
 
-static void pgd_walk_set_prot(void *pt, pgprot_t flags)
-{
-        unsigned long pfn = PFN_DOWN(__pa(pt));
-
-        if (HYPERVISOR_update_va_mapping((unsigned long)pt,
-                                         pfn_pte(pfn, flags), 0) < 0)
-                BUG();
-}
-
-static void pgd_walk(pgd_t *pgd_base, pgprot_t flags)
+/*
+  (Yet another) pagetable walker.  This one is intended for pinning a
+  pagetable.  This means that it walks a pagetable and calls the
+  callback function on each page it finds making up the page table,
+  at every level.  It walks the entire pagetable, but it only bothers
+  pinning pte pages which are below pte_limit.  In the normal case
+  this will be TASK_SIZE, but at boot we need to pin up to
+  FIXADDR_TOP.  But the important bit is that we don't pin beyond
+  there, because then we start getting into Xen's ptes.
+*/
+static int pgd_walk(pgd_t *pgd_base, int (*func)(struct page *, unsigned),
+                    unsigned long limit)
 {
         pgd_t *pgd = pgd_base;
-        pud_t *pud;
-        pmd_t *pmd;
-        pte_t *pte;
-        int    g, u, m;
+        int flush = 0;
+        unsigned long addr = 0;
+        unsigned long pgd_next;
+
+        BUG_ON(limit > FIXADDR_TOP);
 
         if (xen_feature(XENFEAT_auto_translated_physmap))
-                return;
+                return 0;
+
+        for (; addr != FIXADDR_TOP; pgd++, addr = pgd_next) {
+                pud_t *pud;
+                unsigned long pud_limit, pud_next;
 
-        for (g = 0; g < USER_PTRS_PER_PGD; g++, pgd++) {
-                if (pgd_none(*pgd))
+                pgd_next = pud_limit = pgd_addr_end(addr, FIXADDR_TOP);
+
+                if (!pgd_val(*pgd))
                         continue;
+
                 pud = pud_offset(pgd, 0);
 
                 if (PTRS_PER_PUD > 1) /* not folded */
-                        pgd_walk_set_prot(pud, flags);
+                        flush |= (*func)(virt_to_page(pud), 0);
+
+                for (; addr != pud_limit; pud++, addr = pud_next) {
+                        pmd_t *pmd;
+                        unsigned long pmd_limit;
+
+                        pud_next = pud_addr_end(addr, pud_limit);
+
+                        if (pud_next < limit)
+                                pmd_limit = pud_next;
+                        else
+                                pmd_limit = limit;
 
-                for (u = 0; u < PTRS_PER_PUD; u++, pud++) {
                         if (pud_none(*pud))
                                 continue;
+
                         pmd = pmd_offset(pud, 0);
 
                         if (PTRS_PER_PMD > 1) /* not folded */
-                                pgd_walk_set_prot(pmd, flags);
+                                flush |= (*func)(virt_to_page(pmd), 0);
+
+                        for (; addr != pmd_limit; pmd++) {
+                                addr += (PAGE_SIZE * PTRS_PER_PTE);
+                                if ((pmd_limit-1) < (addr-1)) {
+                                        addr = pmd_limit;
+                                        break;
+                                }
 
-                        for (m = 0; m < PTRS_PER_PMD; m++, pmd++) {
                                 if (pmd_none(*pmd))
                                         continue;
 
-                                /* This can get called before mem_map
-                                   is set up, so we assume nothing is
-                                   highmem at that point. */
-                                if (mem_map == NULL ||
-                                    !PageHighMem(pmd_page(*pmd))) {
-                                        pte = pte_offset_kernel(pmd, 0);
-                                        pgd_walk_set_prot(pte, flags);
-                                }
+                                flush |= (*func)(pmd_page(*pmd), 0);
                         }
                 }
         }
 
-        if (HYPERVISOR_update_va_mapping((unsigned long)pgd_base,
-                                         pfn_pte(PFN_DOWN(__pa(pgd_base)),
-                                                 flags),
-                                         UVMF_TLB_FLUSH) < 0)
-                BUG();
+        flush |= (*func)(virt_to_page(pgd_base), UVMF_TLB_FLUSH);
+
+        return flush;
 }
 
+static int pin_page(struct page *page, unsigned flags)
+{
+        unsigned pgfl = test_and_set_bit(PG_pinned, &page->flags);
+        int flush;
+
+        if (pgfl)
+                flush = 0;              /* already pinned */
+        else if (PageHighMem(page))
+                /* kmaps need flushing if we found an unpinned
+                   highpage */
+                flush = 1;
+        else {
+                void *pt = lowmem_page_address(page);
+                unsigned long pfn = page_to_pfn(page);
+                struct multicall_space mcs = __xen_mc_entry(0);
+
+                flush = 0;
+
+                MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
+                                        pfn_pte(pfn, PAGE_KERNEL_RO),
+                                        flags);
+        }
+
+        return flush;
+}
 
-/* This is called just after a mm has been duplicated from its parent,
-   but it has not been used yet.  We need to make sure that its
-   pagetable is all read-only, and can be pinned. */
+/* This is called just after a mm has been created, but it has not
+   been used yet.  We need to make sure that its pagetable is all
+   read-only, and can be pinned. */
 void xen_pgd_pin(pgd_t *pgd)
 {
-        struct mmuext_op op;
+        struct multicall_space mcs;
+        struct mmuext_op *op;
 
-        pgd_walk(pgd, PAGE_KERNEL_RO);
+        xen_mc_batch();
 
-#if defined(CONFIG_X86_PAE)
-        op.cmd = MMUEXT_PIN_L3_TABLE;
+        if (pgd_walk(pgd, pin_page, TASK_SIZE))
+                kmap_flush_unused();
+
+        mcs = __xen_mc_entry(sizeof(*op));
+        op = mcs.args;
+
+#ifdef CONFIG_X86_PAE
+        op->cmd = MMUEXT_PIN_L3_TABLE;
 #else
-        op.cmd = MMUEXT_PIN_L2_TABLE;
+        op->cmd = MMUEXT_PIN_L2_TABLE;
 #endif
-        op.arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(pgd)));
-        if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF) < 0)
-                BUG();
+        op->arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(pgd)));
+        MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
+
+        xen_mc_issue(0);
 }
 
-/* Release a pagetables pages back as normal RW */
-void xen_pgd_unpin(pgd_t *pgd)
+/* The init_mm pagetable is really pinned as soon as its created, but
+   that's before we have page structures to store the bits.  So do all
+   the book-keeping now. */
+static __init int mark_pinned(struct page *page, unsigned flags)
 {
-        struct mmuext_op op;
+        SetPagePinned(page);
+        return 0;
+}
 
-        op.cmd = MMUEXT_UNPIN_TABLE;
-        op.arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(pgd)));
+void __init xen_mark_init_mm_pinned(void)
+{
+        pgd_walk(init_mm.pgd, mark_pinned, FIXADDR_TOP);
+}
 
-        if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF) < 0)
-                BUG();
+static int unpin_page(struct page *page, unsigned flags)
+{
+        unsigned pgfl = test_and_clear_bit(PG_pinned, &page->flags);
 
-        pgd_walk(pgd, PAGE_KERNEL);
+        if (pgfl && !PageHighMem(page)) {
+                void *pt = lowmem_page_address(page);
+                unsigned long pfn = page_to_pfn(page);
+                struct multicall_space mcs = __xen_mc_entry(0);
+
+                MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
+                                        pfn_pte(pfn, PAGE_KERNEL),
+                                        flags);
+        }
+
+        return 0;               /* never need to flush on unpin */
 }
 
+/* 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);
+}
 
 void xen_activate_mm(struct mm_struct *prev, struct mm_struct *next)
 {
+        spin_lock(&next->page_table_lock);
         xen_pgd_pin(next->pgd);
+        spin_unlock(&next->page_table_lock);
 }
 
 void xen_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
 {
+        spin_lock(&mm->page_table_lock);
         xen_pgd_pin(mm->pgd);
+        spin_unlock(&mm->page_table_lock);
 }
 
 void xen_exit_mmap(struct mm_struct *mm)