  We present three-dimensional magnetohydrodynamic (MHD) simulations of the
fueling of supermassive black holes in elliptical galaxies from a turbulent
cooling medium on galactic scales, taking M87* as a typical case. We find that
the mass accretion rate is increased by a factor of $\sim 10$ compared with
analogous hydrodynamic simulations. The scaling of $\dot{M} \sim r^{1/2}$
roughly holds from $\sim 10\,\mathrm{pc}$ to $\sim 10^{-3}\,\mathrm{pc}$ ($\sim
10\, r_\mathrm{g}$) with the accretion rate through the event horizon being
$\sim 10^{-2}\, M_\odot\,\mathrm{yr^{-1}}$. The accretion flow on scales $\sim
0.03-3\,\mathrm{kpc}$ takes the form of magnetized filaments. Within $\sim
30\,\mathrm{pc}$, the cold gas circularizes, forming a highly magnetized
($\beta\sim 10^{-3}$) thick disk supported by a primarily toroidal magnetic
field. The cold disk is truncated and transitions to a turbulent hot accretion
flow at $\sim0.3\,\mathrm{pc}$ ($10^3\,r_\mathrm{g}$). There are strong
outflows towards the poles driven by the magnetic field. The outflow energy
flux increases with smaller accretor size, reaching $\sim
3\times10^{43}\,\mathrm{erg\,s^{-1}}$ for $r_\mathrm{in}=8\,r_\mathrm{g}$; this
corresponds to a nearly constant energy feedback efficiency of
$\eta\sim0.05-0.1$ independent of accretor size. The feedback energy is enough
to balance the total cooling of the M87/Virgo hot halo out to $\sim 50$ kpc.
The accreted magnetic flux at small radii is similar to that in magnetically
arrested disk models, consistent with the formation of a powerful jet on
horizon scales in M87. Our results motivate a subgrid model for accretion in
lower-resolution simulations in which the hot gas accretion rate is suppressed
relative to the Bondi rate by $\sim (10r_\mathrm{g}/r_\mathrm{B})^{1/2}$.
