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Wed, 1 Sep 2021 14:45:11 +0000 (GMT) From: Fabiano Rosas To: Alexey Kardashevskiy , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH kernel] KVM: PPC: Book3S: Suppress failed alloc warning in H_COPY_TOFROM_GUEST In-Reply-To: <20210901084550.1658699-1-aik@ozlabs.ru> References: <20210901084550.1658699-1-aik@ozlabs.ru> Date: Wed, 01 Sep 2021 11:45:09 -0300 Message-ID: <87ilzkuzgq.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-GUID: Tq1OfXfRfWMrsxWWq0Llrcs1zo2g3It0 X-Proofpoint-ORIG-GUID: Tq1OfXfRfWMrsxWWq0Llrcs1zo2g3It0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391, 18.0.790 definitions=2021-09-01_04:2021-09-01, 2021-09-01 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 priorityscore=1501 mlxscore=0 impostorscore=0 suspectscore=0 spamscore=0 lowpriorityscore=0 adultscore=0 clxscore=1015 mlxlogscore=999 phishscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2109010085 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alexey Kardashevskiy , kvm-ppc@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Alexey Kardashevskiy writes: > 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 > --- Reviewed-by: Fabiano Rosas > arch/powerpc/kvm/book3s_hv_nested.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c > index e57c08b968c0..a2e34efb8d31 100644 > --- a/arch/powerpc/kvm/book3s_hv_nested.c > +++ b/arch/powerpc/kvm/book3s_hv_nested.c > @@ -580,7 +580,7 @@ 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;