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Message-ID: <1312888104.26263.99.camel@zakaz.uk.xensource.com>
Date: Tue, 9 Aug 2011 12:08:24 +0100
From: Ian Campbell <Ian.Campbell@...citrix.com>
To: "stefano.stabellini@...citrix.com" <stefano.stabellini@...citrix.com>
CC: "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
"Jeremy Fitzhardinge" <Jeremy.Fitzhardinge@...rix.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen: modify kernel mappings corresponding to granted
pages
On Tue, 2011-07-26 at 17:55 +0100, stefano.stabellini@...citrix.com
wrote:
> From: Stefano Stabellini <stefano.stabellini@...citrix.com>
>
> If we want to use granted pages for AIO, changing the mappings of a user
> vma and the corresponding p2m is not enough, we also need to update the
> kernel mappings accordingly.
> On x86_64 it is easy, we can issue another HYPERVISOR_grant_table_op
> right away in m2p_add_override. We can remove the mappings using another
> HYPERVISOR_grant_table_op in m2p_remove_override.
> On x86_32 it is more difficult because the pages are highmem pages and
> therefore we need to catch the set_pte that tries to map a granted page
> and issue an HYPERVISOR_grant_table_op instead.
> Same thing for unmapping them: we need to catch the pte clear or the
> set_pte that try to unmap a granted page and issue an
> HYPERVISOR_grant_table_op.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> ---
> arch/x86/include/asm/xen/page.h | 5 ++-
> arch/x86/xen/mmu.c | 68 +++++++++++++++++++++++++++++++++++++++
> arch/x86/xen/p2m.c | 47 ++++++++++++++++++++------
> drivers/xen/gntdev.c | 27 +++++++++++++++-
> drivers/xen/grant-table.c | 4 +-
> include/xen/grant_table.h | 1 +
> 6 files changed, 137 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index 64a619d..ec7bbfb 100644
> --- a/arch/x86/include/asm/xen/page.h
> +++ b/arch/x86/include/asm/xen/page.h
> @@ -12,6 +12,7 @@
> #include <asm/pgtable.h>
>
> #include <xen/interface/xen.h>
> +#include <xen/grant_table.h>
> #include <xen/features.h>
>
> /* Xen machine address */
> @@ -31,8 +32,10 @@ typedef struct xpaddr {
> #define INVALID_P2M_ENTRY (~0UL)
> #define FOREIGN_FRAME_BIT (1UL<<(BITS_PER_LONG-1))
> #define IDENTITY_FRAME_BIT (1UL<<(BITS_PER_LONG-2))
> +#define GRANT_FRAME_BIT (1UL<<(BITS_PER_LONG-3))
We need to be a bit careful about stealing more bits from the top of the
MFN space, especially on 32 bit. Stealing the top three bits of a 32 bit
MFN leaves a total (host) address space of 2^(29+12) == 2TB, which seems
large today but... To be honest even the current stealing the top 2 bits
(==8TB) seems a bit shaky for the not too distant future...
I'm not sure what the alternatives are though. Perhaps we can switch
FOREIGN_FRAME_BIT to SOMETHING_SPECIAL_BIT (with a better name ;-)) and
do a secondary lookup based on that? That might be too heavy weight for
FOREIGN and IDENTITY lookups? But for the grant frame bits we are
already manipulating a hashtable too aren't we?
The secondary lookup could be PFN indexed so wouldn't necessarily need
to scale to TB sizes, probably a bitmap would do?
Alternatively perhaps we can reuse the other 31 bits when the
SOMETHING_SPECIAL_BIT is set to indicate what kind of special? e.g.
FOREIGN == 0x80000000, IDENTITY == 0x80000001, GRANT == 0x80000002 etc?
Might interact strangely with the save/restore protocol (ISTR Konrad
investigated that when he added IDENTITY_FRAME_BIT but don't recall the
result).
Ian.
> #define FOREIGN_FRAME(m) ((m) | FOREIGN_FRAME_BIT)
> #define IDENTITY_FRAME(m) ((m) | IDENTITY_FRAME_BIT)
> +#define GRANT_FRAME(m) ((m) | GRANT_FRAME_BIT)
>
> /* Maximum amount of memory we can handle in a domain in pages */
> #define MAX_DOMAIN_PAGES \
> @@ -48,7 +51,7 @@ extern unsigned long set_phys_range_identity(unsigned long pfn_s,
> unsigned long pfn_e);
>
> extern int m2p_add_override(unsigned long mfn, struct page *page,
> - bool clear_pte);
> + struct gnttab_map_grant_ref *kmap_op);
> extern int m2p_remove_override(struct page *page, bool clear_pte);
> extern struct page *m2p_find_override(unsigned long mfn);
> extern unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn);
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 4e37a7c0..13f20d8 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -282,8 +282,70 @@ static bool xen_batched_set_pte(pte_t *ptep, pte_t pteval)
> return true;
> }
>
> +#ifdef CONFIG_HIGHMEM
> +static int xen_unmap_granted_page(pte_t *ptep)
> +{
> + unsigned long mfn;
> + struct page *page;
> +
> + if (pte_flags(*ptep) & _PAGE_USER)
> + return 1;
> + mfn = (ptep->pte & PTE_PFN_MASK) >> PAGE_SHIFT;
> + page = m2p_find_override(mfn);
> + if (page != NULL && (page->private & GRANT_FRAME_BIT)) {
> + int ret;
> + struct gnttab_unmap_grant_ref kunmap_op;
> + struct gnttab_map_grant_ref *kmap_op =
> + (struct gnttab_map_grant_ref *) page->index;
> + kunmap_op.host_addr = kmap_op->host_addr;
> + kunmap_op.handle = kmap_op->handle;
> + kunmap_op.dev_bus_addr = 0;
> + ret = HYPERVISOR_grant_table_op(
> + GNTTABOP_unmap_grant_ref, &kunmap_op, 1);
> + WARN(ret, "m2p_remove_override: pfn %lx mfn %lx, failed to "
> + "modify kernel mappings", page_to_pfn(page), mfn);
> + return ret;
> + }
> + return 1;
> +}
> +#endif
> +
> static void xen_set_pte(pte_t *ptep, pte_t pteval)
> {
> +#ifdef CONFIG_HIGHMEM
> + if (!(pte_flags(pteval) & _PAGE_USER)) {
> + int ret;
> + struct page *page;
> + unsigned long mfn = (pteval.pte & PTE_PFN_MASK) >> PAGE_SHIFT;
> + page = m2p_find_override(mfn);
> + /*
> + * if this is a granted page we need to use a grant table
> + * hypercall to map it instead
> + */
> + if (page != NULL && (page->private & GRANT_FRAME_BIT)) {
> + struct gnttab_map_grant_ref *kmap_op =
> + (struct gnttab_map_grant_ref *) page->index;
> + unsigned long old_mfn = kmap_op->dev_bus_addr;
> + kmap_op->host_addr =
> + arbitrary_virt_to_machine(ptep).maddr;
> + kmap_op->dev_bus_addr = 0;
> + ret = HYPERVISOR_grant_table_op(
> + GNTTABOP_map_grant_ref, kmap_op, 1);
> + WARN(ret, "xen_set_pte: pfn %lx mfn %lx, failed to "
> + "modify kernel mappings",
> + page_to_pfn(page), mfn);
> + kmap_op->dev_bus_addr = old_mfn;
> + return;
> + }
> + /*
> + * even if it is not a granted page, the old page we are about
> + * to overwrite could be a granted page and in that case we need
> + * to unmap it using a grant table hypercall
> + */
> + xen_unmap_granted_page(ptep);
> + }
> +#endif
> +
> if (!xen_batched_set_pte(ptep, pteval))
> native_set_pte(ptep, pteval);
> }
> @@ -548,6 +610,12 @@ static void xen_set_pte_atomic(pte_t *ptep, pte_t pte)
>
> static void xen_pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
> {
> + /*
> + * check if this is a granted page and unmap it using a grant table
> + * hypercall in that case
> + */
> + if (!xen_unmap_granted_page(ptep))
> + return;
> if (!xen_batched_set_pte(ptep, native_make_pte(0)))
> native_pte_clear(mm, addr, ptep);
> }
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 58efeb9..1c4d2b5 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -161,6 +161,7 @@
> #include <asm/xen/page.h>
> #include <asm/xen/hypercall.h>
> #include <asm/xen/hypervisor.h>
> +#include <xen/grant_table.h>
>
> #include "xen-ops.h"
>
> @@ -676,7 +677,8 @@ static unsigned long mfn_hash(unsigned long mfn)
> }
>
> /* Add an MFN override for a particular page */
> -int m2p_add_override(unsigned long mfn, struct page *page, bool clear_pte)
> +int m2p_add_override(unsigned long mfn, struct page *page,
> + struct gnttab_map_grant_ref *kmap_op)
> {
> unsigned long flags;
> unsigned long pfn;
> @@ -699,9 +701,18 @@ int m2p_add_override(unsigned long mfn, struct page *page, bool clear_pte)
> if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn))))
> return -ENOMEM;
>
> - if (clear_pte && !PageHighMem(page))
> - /* Just zap old mapping for now */
> - pte_clear(&init_mm, address, ptep);
> + if (kmap_op != NULL) {
> + if (!PageHighMem(page)) {
> + int ret = HYPERVISOR_grant_table_op(
> + GNTTABOP_map_grant_ref, kmap_op, 1);
> + WARN(ret, "m2p_add_override: pfn %lx mfn %lx, "
> + "failed to modify kernel mappings", pfn, mfn);
> + }
> + page->private |= GRANT_FRAME_BIT;
> + /* let's use dev_bus_addr to record the old mfn instead */
> + kmap_op->dev_bus_addr = page->index;
> + page->index = (unsigned long) kmap_op;
> + }
> spin_lock_irqsave(&m2p_override_lock, flags);
> list_add(&page->lru, &m2p_overrides[mfn_hash(mfn)]);
> spin_unlock_irqrestore(&m2p_override_lock, flags);
> @@ -735,13 +746,27 @@ int m2p_remove_override(struct page *page, bool clear_pte)
> spin_lock_irqsave(&m2p_override_lock, flags);
> list_del(&page->lru);
> spin_unlock_irqrestore(&m2p_override_lock, flags);
> - set_phys_to_machine(pfn, page->index);
>
> - if (clear_pte && !PageHighMem(page))
> - set_pte_at(&init_mm, address, ptep,
> - pfn_pte(pfn, PAGE_KERNEL));
> - /* No tlb flush necessary because the caller already
> - * left the pte unmapped. */
> + 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)) {
> + int ret;
> + struct gnttab_unmap_grant_ref unmap_op;
> + unmap_op.host_addr = map_op->host_addr;
> + unmap_op.handle = map_op->handle;
> + unmap_op.dev_bus_addr = 0;
> + ret = HYPERVISOR_grant_table_op(
> + GNTTABOP_unmap_grant_ref, &unmap_op, 1);
> + WARN(ret, "m2p_remove_override: pfn %lx mfn %lx, "
> + "failed to modify kernel mappings", pfn, mfn);
> + set_pte_at(&init_mm, address, ptep,
> + pfn_pte(pfn, PAGE_KERNEL));
> + __flush_tlb_single(address);
> + }
> + } else
> + set_phys_to_machine(pfn, page->index);
>
> return 0;
> }
> @@ -758,7 +783,7 @@ struct page *m2p_find_override(unsigned long mfn)
> spin_lock_irqsave(&m2p_override_lock, flags);
>
> list_for_each_entry(p, bucket, lru) {
> - if (p->private == mfn) {
> + if ((p->private & (~GRANT_FRAME_BIT)) == mfn) {
> ret = p;
> break;
> }
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index f914b26..ca41772 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -83,6 +83,7 @@ struct grant_map {
> struct ioctl_gntdev_grant_ref *grants;
> struct gnttab_map_grant_ref *map_ops;
> struct gnttab_unmap_grant_ref *unmap_ops;
> + struct gnttab_map_grant_ref *kmap_ops;
> struct page **pages;
> };
>
> @@ -116,10 +117,12 @@ static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
> add->grants = kzalloc(sizeof(add->grants[0]) * count, GFP_KERNEL);
> add->map_ops = kzalloc(sizeof(add->map_ops[0]) * count, GFP_KERNEL);
> add->unmap_ops = kzalloc(sizeof(add->unmap_ops[0]) * count, GFP_KERNEL);
> + add->kmap_ops = kzalloc(sizeof(add->kmap_ops[0]) * count, GFP_KERNEL);
> add->pages = kzalloc(sizeof(add->pages[0]) * count, GFP_KERNEL);
> if (NULL == add->grants ||
> NULL == add->map_ops ||
> NULL == add->unmap_ops ||
> + NULL == add->kmap_ops ||
> NULL == add->pages)
> goto err;
>
> @@ -129,6 +132,7 @@ static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
> for (i = 0; i < count; i++) {
> add->map_ops[i].handle = -1;
> add->unmap_ops[i].handle = -1;
> + add->kmap_ops[i].handle = -1;
> }
>
> add->index = 0;
> @@ -142,6 +146,7 @@ err:
> kfree(add->grants);
> kfree(add->map_ops);
> kfree(add->unmap_ops);
> + kfree(add->kmap_ops);
> kfree(add);
> return NULL;
> }
> @@ -243,10 +248,30 @@ static int map_grant_pages(struct grant_map *map)
> gnttab_set_unmap_op(&map->unmap_ops[i], addr,
> map->flags, -1 /* handle */);
> }
> + } else {
> + for (i = 0; i < map->count; i++) {
> + unsigned level;
> + unsigned long address = (unsigned long)
> + pfn_to_kaddr(page_to_pfn(map->pages[i]));
> + pte_t *ptep;
> + u64 pte_maddr = 0;
> + if (!PageHighMem(map->pages[i])) {
> + ptep = lookup_address(address, &level);
> + pte_maddr =
> + arbitrary_virt_to_machine(ptep).maddr;
> + }
> + gnttab_set_map_op(&map->kmap_ops[i], pte_maddr,
> + map->flags |
> + GNTMAP_host_map |
> + GNTMAP_contains_pte,
> + map->grants[i].ref,
> + map->grants[i].domid);
> + }
> }
>
> pr_debug("map %d+%d\n", map->index, map->count);
> - err = gnttab_map_refs(map->map_ops, map->pages, map->count);
> + err = gnttab_map_refs(map->map_ops, use_ptemod ? map->kmap_ops : NULL,
> + map->pages, map->count);
> if (err)
> return err;
>
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index fd725cd..1e8669a 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -448,6 +448,7 @@ unsigned int gnttab_max_grant_frames(void)
> EXPORT_SYMBOL_GPL(gnttab_max_grant_frames);
>
> int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> + struct gnttab_map_grant_ref *kmap_ops,
> struct page **pages, unsigned int count)
> {
> int i, ret;
> @@ -488,8 +489,7 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> */
> return -EOPNOTSUPP;
> }
> - ret = m2p_add_override(mfn, pages[i],
> - map_ops[i].flags & GNTMAP_contains_pte);
> + ret = m2p_add_override(mfn, pages[i], &kmap_ops[i]);
> if (ret)
> return ret;
> }
> diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
> index b1fab6b..6b99bfb 100644
> --- a/include/xen/grant_table.h
> +++ b/include/xen/grant_table.h
> @@ -156,6 +156,7 @@ unsigned int gnttab_max_grant_frames(void);
> #define gnttab_map_vaddr(map) ((void *)(map.host_virt_addr))
>
> int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
> + struct gnttab_map_grant_ref *kmap_ops,
> struct page **pages, unsigned int count);
> int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
> struct page **pages, unsigned int count);
--
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