This is a note to let you know that I've just added the patch titled KVM: PPC: Book3S: Suppress failed alloc warning in H_COPY_TOFROM_GUEST to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-ppc-book3s-suppress-failed-alloc-warning-in-h_co.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 2c1da3dfd83c301ba283d0dba26a4cb79117b70c Author: Alexey Kardashevskiy <aik@xxxxxxxxx> Date: Wed Sep 1 18:45:50 2021 +1000 KVM: PPC: Book3S: Suppress failed alloc warning in H_COPY_TOFROM_GUEST [ Upstream commit 792020907b11c6f9246c21977cab3bad985ae4b6 ] H_COPY_TOFROM_GUEST is an hcall for an upper level VM to access its nested VMs memory. The userspace can trigger WARN_ON_ONCE(!(gfp & __GFP_NOWARN)) in __alloc_pages() by constructing a tiny VM which only does H_COPY_TOFROM_GUEST with a too big GPR9 (number of bytes to copy). This silences the warning by adding __GFP_NOWARN. Spotted by syzkaller. Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx> Reviewed-by: Fabiano Rosas <farosas@xxxxxxxxxxxxx> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20210901084550.1658699-1-aik@xxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c index ed8a2c9f56299..89295b52a97c3 100644 --- a/arch/powerpc/kvm/book3s_hv_nested.c +++ b/arch/powerpc/kvm/book3s_hv_nested.c @@ -582,7 +582,7 @@ long kvmhv_copy_tofrom_guest_nested(struct kvm_vcpu *vcpu) if (eaddr & (0xFFFUL << 52)) return H_PARAMETER; - buf = kzalloc(n, GFP_KERNEL); + buf = kzalloc(n, GFP_KERNEL | __GFP_NOWARN); if (!buf) return H_NO_MEM;