On 10.01.25 09:48, yangge1116@xxxxxxx wrote:
From: yangge <yangge1116@xxxxxxx>
I would suggest the title to be something like
"KVM: SEV: fix wrong pinning of pages"
Then you can describe that without FOLL_LONGTERM, the pages will not get
migrated out of MIGRATE_CMA/ZONE_MOVABLE, violating these mechanisms to
avoid fragmentation with unmovable pages, for example making CMA
allocations fail.
(CMA allocations failing is only one symptom of the missed usage of
FOLL_LONGTERM)
When pin_user_pages_fast() pins SEV guest memory without the
FOLL_LONGTERM flag, the pinned pages may inadvertently end up in the
CMA (Contiguous Memory Allocator) area. This can subsequently cause
cma_alloc() to fail in allocating these pages, due to the fact that
the pinned pages are not migratable.
To address the aforementioned problem, we propose adding the
FOLL_LONGTERM flag to the pin_user_pages_fast() function. By doing
so, we ensure that the pages allocated will not occupy space within
the CMA area, thereby preventing potential allocation failures.
Signed-off-by: yangge <yangge1116@xxxxxxx>
---
arch/x86/kvm/svm/sev.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 943bd07..35d0714 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -630,6 +630,7 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
unsigned long locked, lock_limit;
struct page **pages;
unsigned long first, last;
+ unsigned int flags = 0;
Why not set
unsigned int flags = FOLL_LONGTERM;
int ret;
lockdep_assert_held(&kvm->lock);
@@ -662,8 +663,10 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
if (!pages)
return ERR_PTR(-ENOMEM);
+ flags = write ? FOLL_WRITE : 0;
and here do
flags |= write ? FOLL_WRITE : 0;
+
/* 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 | FOLL_LONGTERM, pages);
if (npinned != npages) {
pr_err("SEV: Failure locking %lu pages.\n", npages);
ret = -ENOMEM;
--
Cheers,
David / dhildenb
