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    Subject[PATCH AUTOSEL 5.15 14/44] KVM: PPC: Book3S: Suppress failed alloc warning in H_COPY_TOFROM_GUEST
    Date
    From: Alexey Kardashevskiy <aik@ozlabs.ru>

    [ 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@ozlabs.ru>
    Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20210901084550.1658699-1-aik@ozlabs.ru
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 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;

    --
    2.34.1
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