linux-kernel - [PATCH v6 12/22] KVM: Move memslot deletion to helper function

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20200218210736.16432-13-sean.j.christopherson@intel.com>
Date:   Tue, 18 Feb 2020 13:07:26 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        Christoffer Dall <christoffer.dall@....com>,
        Peter Xu <peterx@...hat.com>,
        Philippe Mathieu-Daudé <f4bug@...at.org>
Subject: [PATCH v6 12/22] KVM: Move memslot deletion to helper function

Move memslot deletion into its own routine so that the success path for
other memslot updates does not need to use kvm_free_memslot(), i.e. can
explicitly destroy the dirty bitmap when necessary.  This paves the way
for dropping @dont from kvm_free_memslot(), i.e. all callers now pass
NULL for @dont.

Add a comment above the code to make a copy of the existing memslot
prior to deletion, it is not at all obvious that the pointer will become
stale during sorting and/or installation of new memslots.

Note, kvm_arch_commit_memory_region() allows an architecture to free
resources when moving a memslot or changing its flags, e.g. x86 frees
its arch specific memslot metadata during commit_memory_region().

Acked-by: Christoffer Dall <christoffer.dall@....com>
Tested-by: Christoffer Dall <christoffer.dall@....com>
Reviewed-by: Peter Xu <peterx@...hat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 virt/kvm/kvm_main.c | 75 +++++++++++++++++++++++++++------------------
 1 file changed, 46 insertions(+), 29 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f84bb0442a1b..1f56a0d042a0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1043,6 +1043,27 @@ static int kvm_set_memslot(struct kvm *kvm,
 	return r;
 }
 
+static int kvm_delete_memslot(struct kvm *kvm,
+			      const struct kvm_userspace_memory_region *mem,
+			      struct kvm_memory_slot *old, int as_id)
+{
+	struct kvm_memory_slot new;
+	int r;
+
+	if (!old->npages)
+		return -EINVAL;
+
+	memset(&new, 0, sizeof(new));
+	new.id = old->id;
+
+	r = kvm_set_memslot(kvm, mem, old, &new, as_id, KVM_MR_DELETE);
+	if (r)
+		return r;
+
+	kvm_free_memslot(kvm, old, NULL);
+	return 0;
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -1092,7 +1113,17 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (npages > KVM_MEM_MAX_NR_PAGES)
 		return -EINVAL;
 
-	new = old = *slot;
+	/*
+	 * Make a full copy of the old memslot, the pointer will become stale
+	 * when the memslots are re-sorted by update_memslots(), and the old
+	 * memslot needs to be referenced after calling update_memslots(), e.g.
+	 * to free its resources and for arch specific behavior.
+	 */
+	old = *slot;
+	if (!mem->memory_size)
+		return kvm_delete_memslot(kvm, mem, &old, as_id);
+
+	new = old;
 
 	new.id = id;
 	new.base_gfn = base_gfn;
@@ -1100,29 +1131,20 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	new.flags = mem->flags;
 	new.userspace_addr = mem->userspace_addr;
 
-	if (npages) {
-		if (!old.npages)
-			change = KVM_MR_CREATE;
-		else { /* Modify an existing slot. */
-			if ((new.userspace_addr != old.userspace_addr) ||
-			    (npages != old.npages) ||
-			    ((new.flags ^ old.flags) & KVM_MEM_READONLY))
-				return -EINVAL;
-
-			if (base_gfn != old.base_gfn)
-				change = KVM_MR_MOVE;
-			else if (new.flags != old.flags)
-				change = KVM_MR_FLAGS_ONLY;
-			else /* Nothing to change. */
-				return 0;
-		}
-	} else {
-		if (!old.npages)
+	if (!old.npages) {
+		change = KVM_MR_CREATE;
+	} else { /* Modify an existing slot. */
+		if ((new.userspace_addr != old.userspace_addr) ||
+		    (npages != old.npages) ||
+		    ((new.flags ^ old.flags) & KVM_MEM_READONLY))
 			return -EINVAL;
 
-		change = KVM_MR_DELETE;
-		new.base_gfn = 0;
-		new.flags = 0;
+		if (base_gfn != old.base_gfn)
+			change = KVM_MR_MOVE;
+		else if (new.flags != old.flags)
+			change = KVM_MR_FLAGS_ONLY;
+		else /* Nothing to change. */
+			return 0;
 	}
 
 	if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
@@ -1145,17 +1167,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			return r;
 	}
 
-	/* actual memory is freed via old in kvm_free_memslot below */
-	if (change == KVM_MR_DELETE) {
-		new.dirty_bitmap = NULL;
-		memset(&new.arch, 0, sizeof(new.arch));
-	}
-
 	r = kvm_set_memslot(kvm, mem, &old, &new, as_id, change);
 	if (r)
 		goto out_bitmap;
 
-	kvm_free_memslot(kvm, &old, &new);
+	if (old.dirty_bitmap && !new.dirty_bitmap)
+		kvm_destroy_dirty_bitmap(&old);
 	return 0;
 
 out_bitmap:
-- 
2.24.1