[RFC 16/16] KVM: Unmap protected pages from direct mapping

Kirill A. Shutemov
2020-05-22T12:53:14Z

If the protected memory feature enabled, unmap guest memory from
kernel's direct mappings.

Migration and KSM is disabled for protected memory as it would require a
special treatment.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/mm/pat/set_memory.c | 1 +
include/linux/kvm_host.h | 3 ++
mm/huge_memory.c | 9 +++++
mm/ksm.c | 3 ++
mm/memory.c | 13 +++++++
mm/rmap.c | 4 ++
virt/kvm/kvm_main.c | 74 ++++++++++++++++++++++++++++++++++++
7 files changed, 107 insertions(+)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 6f075766bb94..13988413af40 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2227,6 +2227,7 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)

arch_flush_lazy_mmu_mode();
}
+EXPORT_SYMBOL_GPL(__kernel_map_pages);

#ifdef CONFIG_HIBERNATION
bool kernel_page_present(struct page *page)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b6944f88033d..e1d7762b615c 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -705,6 +705,9 @@ int kvm_protect_all_memory(struct kvm *kvm);
int kvm_protect_memory(struct kvm *kvm,
unsigned long gfn, unsigned long npages, bool protect);

+void kvm_map_page(struct page *page, int nr_pages);
+void kvm_unmap_page(struct page *page, int nr_pages);
+
int gfn_to_page_many_atomic(struct kvm_memory_slot *slot, gfn_t gfn,
struct page **pages, int nr_pages);

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c3562648a4ef..d8a444a401cc 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -33,6 +33,7 @@
#include <linux/oom.h>
#include <linux/numa.h>
#include <linux/page_owner.h>
+#include <linux/kvm_host.h>

#include <asm/tlb.h>
#include <asm/pgalloc.h>
@@ -650,6 +651,10 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
spin_unlock(vmf->ptl);
count_vm_event(THP_FAULT_ALLOC);
count_memcg_events(memcg, THP_FAULT_ALLOC, 1);
+
+ /* Unmap page from direct mapping */
+ if (vma_is_kvm_protected(vma))
+ kvm_unmap_page(page, HPAGE_PMD_NR);
}

return 0;
@@ -1886,6 +1891,10 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
page_remove_rmap(page, true);
VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
VM_BUG_ON_PAGE(!PageHead(page), page);
+
+ /* Map the page back to the direct mapping */
+ if (vma_is_kvm_protected(vma))
+ kvm_map_page(page, HPAGE_PMD_NR);
} else if (thp_migration_supported()) {
swp_entry_t entry;

diff --git a/mm/ksm.c b/mm/ksm.c
index 281c00129a2e..942b88782ac2 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -527,6 +527,9 @@ static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
return NULL;
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
return NULL;
+ /* TODO */
+ if (vma_is_kvm_protected(vma))
+ return NULL;
return vma;
}

diff --git a/mm/memory.c b/mm/memory.c
index d7228db6e4bf..74773229b854 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -71,6 +71,7 @@
#include <linux/dax.h>
#include <linux/oom.h>
#include <linux/numa.h>
+#include <linux/kvm_host.h>

#include <trace/events/kmem.h>

@@ -1088,6 +1089,11 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
likely(!(vma->vm_flags & VM_SEQ_READ)))
mark_page_accessed(page);
}
+
+ /* Map the page back to the direct mapping */
+ if (vma_is_anonymous(vma) && vma_is_kvm_protected(vma))
+ kvm_map_page(page, 1);
+
rss[mm_counter(page)]--;
page_remove_rmap(page, false);
if (unlikely(page_mapcount(page) < 0))
@@ -3312,6 +3318,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
struct page *page;
vm_fault_t ret = 0;
pte_t entry;
+ bool set = false;

/* File mapping without ->vm_ops ? */
if (vma->vm_flags & VM_SHARED)
@@ -3397,6 +3404,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
page_add_new_anon_rmap(page, vma, vmf->address, false);
mem_cgroup_commit_charge(page, memcg, false, false);
lru_cache_add_active_or_unevictable(page, vma);
+ set = true;
setpte:
set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry);

@@ -3404,6 +3412,11 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
update_mmu_cache(vma, vmf->address, vmf->pte);
unlock:
pte_unmap_unlock(vmf->pte, vmf->ptl);
+
+ /* Unmap page from direct mapping */
+ if (vma_is_kvm_protected(vma) && set)
+ kvm_unmap_page(page, 1);
+
return ret;
release:
mem_cgroup_cancel_charge(page, memcg, false);
diff --git a/mm/rmap.c b/mm/rmap.c
index f79a206b271a..a9b2e347d1ab 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1709,6 +1709,10 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,

static bool invalid_migration_vma(struct vm_area_struct *vma, void *arg)
{
+ /* TODO */
+ if (vma_is_kvm_protected(vma))
+ return true;
+
return vma_is_temporary_stack(vma);
}

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 71aac117357f..defc33d3a124 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -51,6 +51,7 @@
#include <linux/io.h>
#include <linux/lockdep.h>
#include <linux/kthread.h>
+#include <linux/pagewalk.h>

#include <asm/processor.h>
#include <asm/ioctl.h>
@@ -2718,6 +2719,72 @@ void kvm_vcpu_mark_page_dirty(struct kvm_vcpu *vcpu, gfn_t gfn)
}
EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty);

+void kvm_map_page(struct page *page, int nr_pages)
+{
+ int i;
+
+ /* Clear page before returning it to the direct mapping */
+ for (i = 0; i < nr_pages; i++) {
+ void *p = map_page_atomic(page + i);
+ memset(p, 0, PAGE_SIZE);
+ unmap_page_atomic(p);
+ }
+
+ kernel_map_pages(page, nr_pages, 1);
+}
+EXPORT_SYMBOL_GPL(kvm_map_page);
+
+void kvm_unmap_page(struct page *page, int nr_pages)
+{
+ kernel_map_pages(page, nr_pages, 0);
+}
+EXPORT_SYMBOL_GPL(kvm_unmap_page);
+
+static int adjust_direct_mapping_pte_range(pmd_t *pmd, unsigned long addr,
+ unsigned long end,
+ struct mm_walk *walk)
+{
+ bool protect = (bool)walk->private;
+ pte_t *pte;
+ struct page *page;
+
+ if (pmd_trans_huge(*pmd)) {
+ page = pmd_page(*pmd);
+ if (is_huge_zero_page(page))
+ return 0;
+ VM_BUG_ON_PAGE(total_mapcount(page) != 1, page);
+ /* XXX: Would it fail with direct device assignment? */
+ VM_BUG_ON_PAGE(page_count(page) != 1, page);
+ kernel_map_pages(page, HPAGE_PMD_NR, !protect);
+ return 0;
+ }
+
+ pte = pte_offset_map(pmd, addr);
+ for (; addr != end; pte++, addr += PAGE_SIZE) {
+ pte_t entry = *pte;
+
+ if (!pte_present(entry))
+ continue;
+
+ if (is_zero_pfn(pte_pfn(entry)))
+ continue;
+
+ page = pte_page(entry);
+
+ VM_BUG_ON_PAGE(page_mapcount(page) != 1, page);
+ /* XXX: Would it fail with direct device assignment? */
+ VM_BUG_ON_PAGE(page_count(page) !=
+ total_mapcount(compound_head(page)), page);
+ kernel_map_pages(page, 1, !protect);
+ }
+
+ return 0;
+}
+
+static const struct mm_walk_ops adjust_direct_mapping_ops = {
+ .pmd_entry = adjust_direct_mapping_pte_range,
+};
+
static int protect_memory(unsigned long start, unsigned long end, bool protect)
{
struct mm_struct *mm = current->mm;
@@ -2763,6 +2830,13 @@ static int protect_memory(unsigned long start, unsigned long end, bool protect)
if (ret)
goto out;

+ if (vma_is_anonymous(vma)) {
+ ret = walk_page_range_novma(mm, start, tmp,
+ &adjust_direct_mapping_ops, NULL,
+ (void *) protect);
+ if (ret)
+ goto out;
+ }
next:
start = tmp;
if (start < prev->vm_end)
--
2.26.2