[PATCH v1 2/2] KVM: s390: pv: fix race when making a page secure

Claudio Imbrenda
2025-02-13T20:08:18Z

Holding the pte lock for the page that is being converted to secure is
needed to avoid races. A previous commit removed the locking, which
caused issues. Fix by locking the pte again.

Fixes: 5cbe24350b7d ("KVM: s390: move pv gmap functions into kvm")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
arch/s390/include/asm/uv.h | 2 +-
arch/s390/kernel/uv.c | 19 +++++++++++++++++--
arch/s390/kvm/gmap.c | 12 ++++++++----
3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
index b11f5b6d0bd1..46fb0ef6f984 100644
--- a/arch/s390/include/asm/uv.h
+++ b/arch/s390/include/asm/uv.h
@@ -631,7 +631,7 @@ int uv_pin_shared(unsigned long paddr);
int uv_destroy_folio(struct folio *folio);
int uv_destroy_pte(pte_t pte);
int uv_convert_from_secure_pte(pte_t pte);
-int make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb);
+int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header *uvcb);
int uv_convert_from_secure(unsigned long paddr);
int uv_convert_from_secure_folio(struct folio *folio);

diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 9f05df2da2f7..de3c092da7b9 100644
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -245,7 +245,7 @@ static int expected_folio_refs(struct folio *folio)
* Context: The caller must hold exactly one extra reference on the folio
* (it's the same logic as split_folio())
*/
-int make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb)
+static int __make_folio_secure(struct folio *folio, unsigned long hva, struct uv_cb_header *uvcb)
{
int expected, cc = 0;

@@ -277,7 +277,22 @@ int make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb)
return -EAGAIN;
return uvcb->rc == 0x10a ? -ENXIO : -EINVAL;
}
-EXPORT_SYMBOL_GPL(make_folio_secure);
+
+int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header *uvcb)
+{
+ spinlock_t *ptelock;
+ pte_t *ptep;
+ int rc;
+
+ ptep = get_locked_pte(mm, hva, &ptelock);
+ if (!ptep)
+ return -ENXIO;
+ rc = __make_folio_secure(page_folio(pte_page(*ptep)), hva, uvcb);
+ pte_unmap_unlock(ptep, ptelock);
+
+ return rc;
+}
+EXPORT_SYMBOL_GPL(make_hva_secure);

/*
* To be called with the folio locked or with an extra reference! This will
diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c
index fc4d490d25a2..e56c0ab5fec7 100644
--- a/arch/s390/kvm/gmap.c
+++ b/arch/s390/kvm/gmap.c
@@ -55,7 +55,7 @@ static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_str
return atomic_read(&mm->context.protected_count) > 1;
}

-static int __gmap_make_secure(struct gmap *gmap, struct page *page, void *uvcb)
+static int __gmap_make_secure(struct gmap *gmap, struct page *page, unsigned long hva, void *uvcb)
{
struct folio *folio = page_folio(page);
int rc;
@@ -83,7 +83,7 @@ static int __gmap_make_secure(struct gmap *gmap, struct page *page, void *uvcb)
return -EAGAIN;
if (should_export_before_import(uvcb, gmap->mm))
uv_convert_from_secure(folio_to_phys(folio));
- rc = make_folio_secure(folio, uvcb);
+ rc = make_hva_secure(gmap->mm, hva, uvcb);
folio_unlock(folio);

/*
@@ -120,6 +120,7 @@ static int __gmap_make_secure(struct gmap *gmap, struct page *page, void *uvcb)
int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
{
struct kvm *kvm = gmap->private;
+ unsigned long vmaddr;
struct page *page;
int rc = 0;

@@ -127,8 +128,11 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)

page = gfn_to_page(kvm, gpa_to_gfn(gaddr));
mmap_read_lock(gmap->mm);
- if (page)
- rc = __gmap_make_secure(gmap, page, uvcb);
+ vmaddr = gfn_to_hva(gmap->private, gpa_to_gfn(gaddr));
+ if (kvm_is_error_hva(vmaddr))
+ rc = -ENXIO;
+ if (!rc && page)
+ rc = __gmap_make_secure(gmap, page, vmaddr, uvcb);
kvm_release_page_clean(page);
mmap_read_unlock(gmap->mm);

--
2.48.1