This is the kvm.git patch to enable -reserved-ram (without this kvm
will simply gracefully fail to emulate the illegal instruction inside
the bad_page). This trick avoids altering the ioctl api with libkvm,
in short if get_user_pages fails on a host kernel with reserved ram
config option enabled, it tries to see if it's a remap_pfn_range
mapping backing the memslot. In such case it checks if the ram was
reserved with page_count 0 and if so it disables the reference
counting as those pages are invisibile to linux. As long as pfn_valid
returns, pfn_to_page should be safe, so shall the memmap array be
allocated with holes corresponding to the holes generated in the e820
map, simply bad_page will be returned gracefully without risk like if
this patch wasn't applied to kvm.git.
Signed-off-by: Andrea Arcangeli <[EMAIL PROTECTED]>
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index e9ae5db..e7a9c82 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -263,7 +263,8 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct
kvm_mmu_page *page,
npage = vcpu->arch.update_pte.page;
if (!npage)
return;
- get_page(npage);
+ if (!page_is_reserved(npage))
+ get_page(npage);
mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,
gpte & PT_DIRTY_MASK, NULL, largepage, gpte_to_gfn(gpte),
npage, true);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f4e1436..7f087ac 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -281,6 +281,18 @@ static inline void kvm_migrate_apic_timer(struct kvm_vcpu
*vcpu)
set_bit(KVM_REQ_MIGRATE_TIMER, &vcpu->requests);
}
+#ifdef CONFIG_RESERVE_PHYSICAL_START
+static inline int page_is_reserved(struct page * page)
+{
+ return !page_count(page);
+}
+#else /* CONFIG_RESERVE_PHYSICAL_START */
+static inline int page_is_reserved(struct page * page)
+{
+ return 0;
+}
+#endif /* CONFIG_RESERVE_PHYSICAL_START */
+
enum kvm_stat_kind {
KVM_STAT_VM,
KVM_STAT_VCPU,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 30bf832..50a7b3e 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -498,6 +524,65 @@ unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
return (slot->userspace_addr + (gfn - slot->base_gfn) * PAGE_SIZE);
}
+
+#ifdef CONFIG_RESERVE_PHYSICAL_START
+static struct page *direct_page(struct mm_struct *mm,
+ unsigned long address)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *ptep, pte;
+ spinlock_t *ptl;
+ struct page *page;
+ struct vm_area_struct *vma;
+ unsigned long pfn;
+
+ page = NULL;
+ if (!capable(CAP_SYS_ADMIN)) /* go safe */
+ goto out;
+
+ vma = find_vma(current->mm, address);
+ if (!vma || vma->vm_start > address ||
+ !(vma->vm_flags & VM_PFNMAP))
+ goto out;
+
+ pgd = pgd_offset(mm, address);
+ if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+ goto out;
+
+ pud = pud_offset(pgd, address);
+ if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+ goto out;
+
+ pmd = pmd_offset(pud, address);
+ if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+ goto out;
+
+ ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
+ if (!ptep)
+ goto out;
+
+ pte = *ptep;
+ if (!pte_present(pte))
+ goto unlock;
+
+ pfn = pte_pfn(pte);
+ if (!pfn_valid(pfn))
+ goto unlock;
+
+ page = pfn_to_page(pfn);
+ if (!page_is_reserved(page)) {
+ page = NULL;
+ goto unlock;
+ }
+unlock:
+ pte_unmap_unlock(ptep, ptl);
+out:
+ return page;
+}
+#endif /* CONFIG_RESERVE_PHYSICAL_START */
+
/*
* Requires current->mm->mmap_sem to be held
*/
@@ -519,6 +604,11 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
NULL);
if (npages != 1) {
+#ifdef CONFIG_RESERVE_PHYSICAL_START
+ page[0] = direct_page(current->mm, addr);
+ if (page[0])
+ return page[0];
+#endif
get_page(bad_page);
return bad_page;
}
@@ -530,15 +620,18 @@ EXPORT_SYMBOL_GPL(gfn_to_page);
void kvm_release_page_clean(struct page *page)
{
- put_page(page);
+ if (!page_is_reserved(page))
+ put_page(page);
}
EXPORT_SYMBOL_GPL(kvm_release_page_clean);
void kvm_release_page_dirty(struct page *page)
{
- if (!PageReserved(page))
- SetPageDirty(page);
- put_page(page);
+ if (!page_is_reserved(page)) {
+ if (!PageReserved(page))
+ SetPageDirty(page);
+ put_page(page);
+ }
}
EXPORT_SYMBOL_GPL(kvm_release_page_dirty);
-------------------------------------------------------------------------
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