From: Ge Yang <yangge1116@126.com>

In the sev_mem_enc_register_region() function, we need to call
sev_pin_memory() to pin memory for the long term. However, when
calling sev_pin_memory(), the FOLL_LONGTERM flag is not passed, causing
the allocated pages not to be migrated out of MIGRATE_CMA/ZONE_MOVABLE,
violating these mechanisms to avoid fragmentation with unmovable pages,
for example making CMA allocations fail.

To address the aforementioned problem, we should add the FOLL_LONGTERM
flag when calling sev_pin_memory() within the sev_mem_enc_register_region()
function.

Signed-off-by: Ge Yang <yangge1116@126.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
---

V4:
- adjust the code format suggested by Tom

V3:
- the fix only needed for sev_mem_enc_register_region()

V2:
- update code and commit message suggested by David

 arch/x86/kvm/svm/sev.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index a2a794c..90ad846 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -622,7 +622,7 @@ static int sev_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
 
 static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
 				    unsigned long ulen, unsigned long *n,
-				    int write)
+				    int flags)
 {
 	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
 	unsigned long npages, size;
@@ -663,7 +663,7 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
 		return ERR_PTR(-ENOMEM);
 
 	/* Pin the user virtual address. */
-	npinned = pin_user_pages_fast(uaddr, npages, write ? FOLL_WRITE : 0, pages);
+	npinned = pin_user_pages_fast(uaddr, npages, flags, pages);
 	if (npinned != npages) {
 		pr_err("SEV: Failure locking %lu pages.\n", npages);
 		ret = -ENOMEM;
@@ -751,7 +751,7 @@ static int sev_launch_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	vaddr_end = vaddr + size;
 
 	/* Lock the user memory. */
-	inpages = sev_pin_memory(kvm, vaddr, size, &npages, 1);
+	inpages = sev_pin_memory(kvm, vaddr, size, &npages, FOLL_WRITE);
 	if (IS_ERR(inpages))
 		return PTR_ERR(inpages);
 
@@ -1250,7 +1250,7 @@ static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec)
 		if (IS_ERR(src_p))
 			return PTR_ERR(src_p);
 
-		dst_p = sev_pin_memory(kvm, dst_vaddr & PAGE_MASK, PAGE_SIZE, &n, 1);
+		dst_p = sev_pin_memory(kvm, dst_vaddr & PAGE_MASK, PAGE_SIZE, &n, FOLL_WRITE);
 		if (IS_ERR(dst_p)) {
 			sev_unpin_memory(kvm, src_p, n);
 			return PTR_ERR(dst_p);
@@ -1316,7 +1316,7 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	if (copy_from_user(&params, u64_to_user_ptr(argp->data), sizeof(params)))
 		return -EFAULT;
 
-	pages = sev_pin_memory(kvm, params.guest_uaddr, params.guest_len, &n, 1);
+	pages = sev_pin_memory(kvm, params.guest_uaddr, params.guest_len, &n, FOLL_WRITE);
 	if (IS_ERR(pages))
 		return PTR_ERR(pages);
 
@@ -1798,7 +1798,7 @@ static int sev_receive_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
 
 	/* Pin guest memory */
 	guest_page = sev_pin_memory(kvm, params.guest_uaddr & PAGE_MASK,
-				    PAGE_SIZE, &n, 1);
+				    PAGE_SIZE, &n, FOLL_WRITE);
 	if (IS_ERR(guest_page)) {
 		ret = PTR_ERR(guest_page);
 		goto e_free_trans;
@@ -2696,7 +2696,8 @@ int sev_mem_enc_register_region(struct kvm *kvm,
 		return -ENOMEM;
 
 	mutex_lock(&kvm->lock);
-	region->pages = sev_pin_memory(kvm, range->addr, range->size, &region->npages, 1);
+	region->pages = sev_pin_memory(kvm, range->addr, range->size, &region->npages,
+				       FOLL_WRITE | FOLL_LONGTERM);
 	if (IS_ERR(region->pages)) {
 		ret = PTR_ERR(region->pages);
 		mutex_unlock(&kvm->lock);
-- 
2.7.4

On Tue, 11 Feb 2025 10:37:03 +0800, yangge1116@126.com wrote:
> In the sev_mem_enc_register_region() function, we need to call
> sev_pin_memory() to pin memory for the long term. However, when
> calling sev_pin_memory(), the FOLL_LONGTERM flag is not passed, causing
> the allocated pages not to be migrated out of MIGRATE_CMA/ZONE_MOVABLE,
> violating these mechanisms to avoid fragmentation with unmovable pages,
> for example making CMA allocations fail.
> 
> [...]

Applied to kvm-x86 svm, thanks!

[1/1] KVM: SEV: fix wrong pinning of pages
      https://github.com/kvm-x86/linux/commit/7e066cb9b71a

--
https://github.com/kvm-x86/linux/tree/next

On 11.02.25 03:37, yangge1116@126.com wrote:
> From: Ge Yang <yangge1116@126.com>
> 
> In the sev_mem_enc_register_region() function, we need to call
> sev_pin_memory() to pin memory for the long term. However, when
> calling sev_pin_memory(), the FOLL_LONGTERM flag is not passed, causing
> the allocated pages not to be migrated out of MIGRATE_CMA/ZONE_MOVABLE,
> violating these mechanisms to avoid fragmentation with unmovable pages,
> for example making CMA allocations fail.
> 
> To address the aforementioned problem, we should add the FOLL_LONGTERM
> flag when calling sev_pin_memory() within the sev_mem_enc_register_region()
> function.
> 
> Signed-off-by: Ge Yang <yangge1116@126.com>
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb