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Subject[PATCH 50/50] KVM: Allocate userspace memory for older userspace
Date
From: Anthony Liguori <aliguori@us.ibm.com>

Allocate a userspace buffer for older userspaces. Also eliminate phys_mem
buffer. The memset() in kvmctl really kills initial memory usage but swapping
works even with old userspaces.

A side effect is that maximum guest side is reduced for older userspace on
i386.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
---
drivers/kvm/kvm.h | 2 -
drivers/kvm/kvm_main.c | 83 +++++++++++++++++------------------------------
2 files changed, 30 insertions(+), 55 deletions(-)
diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index e8a21e8..eb006ed 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -406,10 +406,8 @@ struct kvm_memory_slot {
gfn_t base_gfn;
unsigned long npages;
unsigned long flags;
- struct page **phys_mem;
unsigned long *rmap;
unsigned long *dirty_bitmap;
- int user_alloc; /* user allocated memory */
unsigned long userspace_addr;
};

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 1c64047..3aec716 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -42,6 +42,7 @@
#include <linux/profile.h>
#include <linux/kvm_para.h>
#include <linux/pagemap.h>
+#include <linux/mman.h>

#include <asm/processor.h>
#include <asm/msr.h>
@@ -300,36 +301,21 @@ static struct kvm *kvm_create_vm(void)
return kvm;
}

-static void kvm_free_kernel_physmem(struct kvm_memory_slot *free)
-{
- int i;
-
- for (i = 0; i < free->npages; ++i)
- if (free->phys_mem[i])
- __free_page(free->phys_mem[i]);
-}
-
/*
* Free any memory in @free but not in @dont.
*/
static void kvm_free_physmem_slot(struct kvm_memory_slot *free,
struct kvm_memory_slot *dont)
{
- if (!dont || free->phys_mem != dont->phys_mem)
- if (free->phys_mem) {
- if (!free->user_alloc)
- kvm_free_kernel_physmem(free);
- vfree(free->phys_mem);
- }
if (!dont || free->rmap != dont->rmap)
vfree(free->rmap);

if (!dont || free->dirty_bitmap != dont->dirty_bitmap)
vfree(free->dirty_bitmap);

- free->phys_mem = NULL;
free->npages = 0;
free->dirty_bitmap = NULL;
+ free->rmap = NULL;
}

static void kvm_free_physmem(struct kvm *kvm)
@@ -712,10 +698,6 @@ static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
goto out_unlock;
}

- /* Deallocate if slot is being removed */
- if (!npages)
- new.phys_mem = NULL;
-
/* Free page dirty bitmap if unneeded */
if (!(new.flags & KVM_MEM_LOG_DIRTY_PAGES))
new.dirty_bitmap = NULL;
@@ -723,29 +705,27 @@ static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
r = -ENOMEM;

/* Allocate if a slot is being created */
- if (npages && !new.phys_mem) {
- new.phys_mem = vmalloc(npages * sizeof(struct page *));
-
- if (!new.phys_mem)
- goto out_unlock;
-
+ if (npages && !new.rmap) {
new.rmap = vmalloc(npages * sizeof(struct page *));

if (!new.rmap)
goto out_unlock;

- memset(new.phys_mem, 0, npages * sizeof(struct page *));
memset(new.rmap, 0, npages * sizeof(*new.rmap));
- if (user_alloc) {
- new.user_alloc = 1;
+
+ if (user_alloc)
new.userspace_addr = mem->userspace_addr;
- } else {
- for (i = 0; i < npages; ++i) {
- new.phys_mem[i] = alloc_page(GFP_HIGHUSER
- | __GFP_ZERO);
- if (!new.phys_mem[i])
- goto out_unlock;
- }
+ else {
+ down_write(&current->mm->mmap_sem);
+ new.userspace_addr = do_mmap(NULL, 0,
+ npages * PAGE_SIZE,
+ PROT_READ | PROT_WRITE,
+ MAP_SHARED | MAP_ANONYMOUS,
+ 0);
+ up_write(&current->mm->mmap_sem);
+
+ if (IS_ERR((void *)new.userspace_addr))
+ goto out_unlock;
}
}

@@ -1010,6 +990,8 @@ struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
{
struct kvm_memory_slot *slot;
+ struct page *page[1];
+ int npages;

gfn = unalias_gfn(kvm, gfn);
slot = __gfn_to_memslot(kvm, gfn);
@@ -1017,24 +999,19 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
get_page(bad_page);
return bad_page;
}
- if (slot->user_alloc) {
- struct page *page[1];
- int npages;
-
- down_read(&current->mm->mmap_sem);
- npages = get_user_pages(current, current->mm,
- slot->userspace_addr
- + (gfn - slot->base_gfn) * PAGE_SIZE, 1,
- 1, 0, page, NULL);
- up_read(&current->mm->mmap_sem);
- if (npages != 1) {
- get_page(bad_page);
- return bad_page;
- }
- return page[0];
+
+ down_read(&current->mm->mmap_sem);
+ npages = get_user_pages(current, current->mm,
+ slot->userspace_addr
+ + (gfn - slot->base_gfn) * PAGE_SIZE, 1,
+ 1, 0, page, NULL);
+ up_read(&current->mm->mmap_sem);
+ if (npages != 1) {
+ get_page(bad_page);
+ return bad_page;
}
- get_page(slot->phys_mem[gfn - slot->base_gfn]);
- return slot->phys_mem[gfn - slot->base_gfn];
+
+ return page[0];
}
EXPORT_SYMBOL_GPL(gfn_to_page);

--
1.5.3.7


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