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@xxxxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
Cc: Zach Amsden <zach@xxxxxxxxxx>
---
arch/i386/xen/enlighten.c | 107 ++++++++++++----
arch/i386/xen/mmu.c | 286 ++++++++++++++++++++++++++++-----------------
arch/i386/xen/mmu.h | 2
arch/i386/xen/xen-ops.h | 2
4 files changed, 265 insertions(+), 132 deletions(-)
===================================================================
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -21,6 +21,9 @@
#include <linux/sched.h>
#include <linux/bootmem.h>
#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/page-flags.h>
+#include <linux/highmem.h>
#include <xen/interface/xen.h>
#include <xen/interface/physdev.h>
@@ -500,32 +503,59 @@ static void xen_write_cr3(unsigned long
}
}
+/* Early in boot, while setting up the initial pagetable, assume
+ everything is pinned. */
+static void xen_alloc_pt_init(struct mm_struct *mm, u32 pfn)
+{
+ BUG_ON(mem_map); /* should only be used early */
+ make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
+}
+
+/* This needs to make sure the new pte page is pinned iff its being
+ attached to a pinned pagetable. */
static void xen_alloc_pt(struct mm_struct *mm, u32 pfn)
{
- /* XXX pfn isn't necessarily a lowmem page */
- make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
-}
-
-static void xen_alloc_pd(u32 pfn)
-{
- make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
-}
-
-static void xen_release_pd(u32 pfn)
-{
- make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
-}
-
+ struct page *page = pfn_to_page(pfn);
+
+ if (PagePinned(virt_to_page(mm->pgd))) {
+ SetPagePinned(page);
+
+ if (!PageHighMem(page))
+ make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
+ else
+ /* make sure there are no stray mappings of
+ this page */
+ kmap_flush_unused();
+ }
+}
+
+/* This should never happen until we're OK to use struct page */
static void xen_release_pt(u32 pfn)
{
- make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
-}
-
-static void xen_alloc_pd_clone(u32 pfn, u32 clonepfn,
- u32 start, u32 count)
-{
- xen_alloc_pd(pfn);
-}
+ struct page *page = pfn_to_page(pfn);
+
+ if (PagePinned(page)) {
+ if (!PageHighMem(page))
+ make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
+ }
+}
+
+#ifdef CONFIG_HIGHPTE
+static void *xen_kmap_atomic_pte(struct page *page, enum km_type type)
+{
+ pgprot_t prot = PAGE_KERNEL;
+
+ if (PagePinned(page))
+ prot = PAGE_KERNEL_RO;
+
+ if (0 && PageHighMem(page))
+ printk("mapping highpte %lx type %d prot %s\n",
+ page_to_pfn(page), type,
+ (unsigned long)pgprot_val(prot) & _PAGE_RW ? "WRITE" :
"READ");
+
+ return kmap_atomic_prot(page, type, prot);
+}
+#endif
static __init void xen_pagetable_setup_start(pgd_t *base)
{
@@ -553,7 +583,7 @@ static __init void xen_pagetable_setup_s
memcpy(pmd, (void *)pgd_page_vaddr(xen_pgd[i]),
PAGE_SIZE);
- xen_alloc_pd(PFN_DOWN(__pa(pmd)));
+ make_lowmem_page_readonly(pmd);
set_pgd(&base[i], __pgd(1 + __pa(pmd)));
} else
@@ -574,6 +604,10 @@ static __init void xen_pagetable_setup_s
static __init void xen_pagetable_setup_done(pgd_t *base)
{
+ /* This will work as long as patching hasn't happened yet
+ (which it hasn't) */
+ paravirt_ops.alloc_pt = xen_alloc_pt;
+
if (!xen_feature(XENFEAT_auto_translated_physmap)) {
/*
* Create a mapping for the shared info page.
@@ -591,7 +625,19 @@ static __init void xen_pagetable_setup_d
HYPERVISOR_shared_info =
(struct shared_info *)__va(xen_start_info->shared_info);
- xen_pgd_pin(base);
+ /* Actually pin the pagetable down, but we can't set PG_pinned
+ yet because the page structures don't exist yet. */
+ {
+ struct mmuext_op op;
+#ifdef CONFIG_X86_PAE
+ op.cmd = MMUEXT_PIN_L3_TABLE;
+#else
+ op.cmd = MMUEXT_PIN_L3_TABLE;
+#endif
+ op.arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(base)));
+ if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
+ BUG();
+ }
xen_vcpu_setup(smp_processor_id());
}
@@ -608,6 +654,7 @@ static const struct paravirt_ops xen_par
.memory_setup = xen_memory_setup,
.arch_setup = xen_arch_setup,
.init_IRQ = xen_init_IRQ,
+ .post_allocator_init = xen_mark_init_mm_pinned,
.time_init = xen_time_init,
.set_wallclock = xen_set_wallclock,
@@ -688,11 +735,15 @@ static const struct paravirt_ops xen_par
.pagetable_setup_start = xen_pagetable_setup_start,
.pagetable_setup_done = xen_pagetable_setup_done,
- .alloc_pt = xen_alloc_pt,
- .alloc_pd = xen_alloc_pd,
- .alloc_pd_clone = xen_alloc_pd_clone,
- .release_pd = xen_release_pd,
+ .alloc_pt = xen_alloc_pt_init,
.release_pt = xen_release_pt,
+ .alloc_pd = paravirt_nop,
+ .alloc_pd_clone = paravirt_nop,
+ .release_pd = paravirt_nop,
+
+#ifdef CONFIG_HIGHPTE
+ .kmap_atomic_pte = xen_kmap_atomic_pte,
+#endif
.set_pte = xen_set_pte,
.set_pte_at = xen_set_pte_at,
===================================================================
--- a/arch/i386/xen/mmu.c
+++ b/arch/i386/xen/mmu.c
@@ -38,19 +38,22 @@
*
* Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>, 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)
@@ -91,16 +94,6 @@ void make_lowmem_page_readwrite(void *va
BUG();
}
-
-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)
{
@@ -111,18 +104,6 @@ void xen_set_pmd(pmd_t *ptr, pmd_t val)
if (HYPERVISOR_mmu_update(&u, 1, NULL, DOMID_SELF) < 0)
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
@@ -170,6 +151,23 @@ void xen_set_pte_at(struct mm_struct *mm
}
#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 pg
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;
@@ -247,13 +250,6 @@ unsigned long xen_pte_val(pte_t pte)
ret = machine_to_phys(XMADDR(ret)).paddr;
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)
@@ -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;
-
- for (g = 0; g < USER_PTRS_PER_PGD; g++, pgd++) {
- if (pgd_none(*pgd))
+ return 0;
+
+ for (; addr != FIXADDR_TOP; pgd++, addr = pgd_next) {
+ pud_t *pud;
+ unsigned long pud_limit, pud_next;
+
+ 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);
-
- for (u = 0; u < PTRS_PER_PUD; u++, pud++) {
+ 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;
+
if (pud_none(*pud))
continue;
+
pmd = pmd_offset(pud, 0);
if (PTRS_PER_PMD > 1) /* not folded */
- pgd_walk_set_prot(pmd, flags);
-
- for (m = 0; m < PTRS_PER_PMD; m++, pmd++) {
+ 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;
+ }
+
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();
-}
-
-
-/* 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. */
+ 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 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;
-
- pgd_walk(pgd, PAGE_KERNEL_RO);
-
-#if defined(CONFIG_X86_PAE)
- op.cmd = MMUEXT_PIN_L3_TABLE;
+ struct multicall_space mcs;
+ struct mmuext_op *op;
+
+ xen_mc_batch();
+
+ 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);
+}
+
+/* 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)
+{
+ SetPagePinned(page);
+ return 0;
+}
+
+void __init xen_mark_init_mm_pinned(void)
+{
+ pgd_walk(init_mm.pgd, mark_pinned, FIXADDR_TOP);
+}
+
+static int unpin_page(struct page *page, unsigned flags)
+{
+ unsigned pgfl = test_and_clear_bit(PG_pinned, &page->flags);
+
+ 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 */
-void xen_pgd_unpin(pgd_t *pgd)
-{
- struct mmuext_op op;
-
- op.cmd = MMUEXT_UNPIN_TABLE;
- op.arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(pgd)));
-
- if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF) < 0)
- BUG();
-
- pgd_walk(pgd, PAGE_KERNEL);
-}
-
+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)
===================================================================
--- a/arch/i386/xen/mmu.h
+++ b/arch/i386/xen/mmu.h
@@ -15,7 +15,7 @@ void xen_exit_mmap(struct mm_struct *mm)
void xen_exit_mmap(struct mm_struct *mm);
void xen_pgd_pin(pgd_t *pgd);
-void xen_pgd_unpin(pgd_t *pgd);
+//void xen_pgd_unpin(pgd_t *pgd);
#ifdef CONFIG_X86_PAE
unsigned long long xen_pte_val(pte_t);
===================================================================
--- a/arch/i386/xen/xen-ops.h
+++ b/arch/i386/xen/xen-ops.h
@@ -20,6 +20,8 @@ int xen_set_wallclock(unsigned long time
int xen_set_wallclock(unsigned long time);
cycle_t xen_clocksource_read(void);
+void xen_mark_init_mm_pinned(void);
+
DECLARE_PER_CPU(enum paravirt_lazy_mode, xen_lazy_mode);
static inline unsigned xen_get_lazy_mode(void)
--
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