Calls to idr_alloc() in __prealloc_nested() are not currently synchronized.
According to the documentation [1], the caller should provide their own
locking to prevent concurrent modifications to the idr to prevent bugs.
__prealloc_nested() calls idr_alloc() with GFP_KERNEL which can
sleep and mmu_lock is a spinlock. So idr_alloc() cannot be moved under
mmu_lock. In such cases the idr Documentation says:
If you need to take a lock while allocating a new ID from the IDR,
you may need to pass a restrictive set of GFP flags, which can lead
to the IDR being unable to allocate memory. To work around this,
you can call idr_preload() before taking the lock, and then
idr_preload_end() after the allocation.
Hence preload the idr memory with idr_preload() before taking mmu_lock,
which allows us to use idr_alloc(..., GFP_NOWAIT) under the spinlock.
This also allows to kill __prealloc_nested() and __add_nested(), as they
are not needed anymore with idr_preload().
[1]: lib/idr.c
Fixes: c0f00a18e2a8 ("KVM: PPC: Book3S HV Nested: Change nested guest lookup to
use idr")
Cc: [email protected] # 5.19+
Co-developed-by: Ritesh Harjani (IBM) <[email protected]>
Signed-off-by: Ritesh Harjani (IBM) <[email protected]>
Signed-off-by: Gautam Menghani <[email protected]>
---
v3:
1. Fix the patch description to accurately describe the code change.
(Ritesh)
v2:
1. None
arch/powerpc/kvm/book3s_hv_nested.c | 34 +++++++++--------------------
1 file changed, 10 insertions(+), 24 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_nested.c
b/arch/powerpc/kvm/book3s_hv_nested.c
index a6ff42d7666c..e893fdd24f0a 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -702,20 +702,6 @@ static struct kvm_nested_guest *__find_nested(struct kvm
*kvm, int lpid)
return idr_find(&kvm->arch.kvm_nested_guest_idr, lpid);
}
-static bool __prealloc_nested(struct kvm *kvm, int lpid)
-{
- if (idr_alloc(&kvm->arch.kvm_nested_guest_idr,
- NULL, lpid, lpid + 1, GFP_KERNEL) != lpid)
- return false;
- return true;
-}
-
-static void __add_nested(struct kvm *kvm, int lpid, struct kvm_nested_guest
*gp)
-{
- if (idr_replace(&kvm->arch.kvm_nested_guest_idr, gp, lpid))
- WARN_ON(1);
-}
-
static void __remove_nested(struct kvm *kvm, int lpid)
{
idr_remove(&kvm->arch.kvm_nested_guest_idr, lpid);
@@ -862,21 +848,21 @@ struct kvm_nested_guest *kvmhv_get_nested(struct kvm
*kvm, int l1_lpid,
if (!newgp)
return NULL;
- if (!__prealloc_nested(kvm, l1_lpid)) {
- kvmhv_release_nested(newgp);
- return NULL;
- }
-
+ idr_preload(GFP_KERNEL);
spin_lock(&kvm->mmu_lock);
gp = __find_nested(kvm, l1_lpid);
if (!gp) {
- __add_nested(kvm, l1_lpid, newgp);
- ++newgp->refcnt;
- gp = newgp;
- newgp = NULL;
+ if (idr_alloc(&kvm->arch.kvm_nested_guest_idr, newgp,
+ l1_lpid, l1_lpid + 1, GFP_NOWAIT) >= 0) {
+ ++newgp->refcnt;
+ gp = newgp;
+ newgp = NULL;
+ }
}
- ++gp->refcnt;
+ if (gp)
+ ++gp->refcnt;
spin_unlock(&kvm->mmu_lock);
+ idr_preload_end();
if (newgp)
kvmhv_release_nested(newgp);
--
2.54.0
