Re: [PATCH v4 4/6] hw/arm/virt: Use the PA range to compute the memory map

[Marc Zyngier]

On Mon, 10 Jan 2022 15:38:56 +0000,
Eric Auger <eric.auger@redhat.com> wrote:
> 
> Hi Marc,
> 
> On 1/7/22 5:33 PM, Marc Zyngier wrote:
> > The highmem attribute is nothing but another way to express the
> > PA range of a VM. To support HW that has a smaller PA range then
> > what QEMU assumes, pass this PA range to the virt_set_memmap()
> > function, allowing it to correctly exclude highmem devices
> > if they are outside of the PA range.
> >
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  hw/arm/virt.c | 53 ++++++++++++++++++++++++++++++++++++++++++++-------
> >  1 file changed, 46 insertions(+), 7 deletions(-)
> >
> > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > index 57c55e8a37..db4b0636e1 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -1660,7 +1660,7 @@ static uint64_t virt_cpu_mp_affinity(VirtMachineState 
> > *vms, int idx)
> >      return arm_cpu_mp_affinity(idx, clustersz);
> >  }
> >  
> > -static void virt_set_memmap(VirtMachineState *vms)
> > +static void virt_set_memmap(VirtMachineState *vms, int pa_bits)
> >  {
> >      MachineState *ms = MACHINE(vms);
> >      hwaddr base, device_memory_base, device_memory_size, memtop;
> > @@ -1678,6 +1678,13 @@ static void virt_set_memmap(VirtMachineState *vms)
> >          exit(EXIT_FAILURE);
> >      }
> >  
> > +    /*
> > +     * !highmem is exactly the same as limiting the PA space to 32bit,
> > +     * irrespective of the underlying capabilities of the HW.
> > +     */
> > +    if (!vms->highmem)
> > +       pa_bits = 32;
> you need {} according to the QEMU coding style. Welcome to a new shiny
> world :-)

Yeah. Between the reduced indentation and the avalanche of braces, my
brain fails to pattern-match blocks of code. Amusing how inflexible
you become after a couple of decades...

> > +
> >      /*
> >       * We compute the base of the high IO region depending on the
> >       * amount of initial and device memory. The device memory start/size
> > @@ -1691,8 +1698,9 @@ static void virt_set_memmap(VirtMachineState *vms)
> >  
> >      /* Base address of the high IO region */
> >      memtop = base = device_memory_base + ROUND_UP(device_memory_size, GiB);
> > -    if (!vms->highmem && memtop > 4 * GiB) {
> > -        error_report("highmem=off, but memory crosses the 4GiB limit\n");
> > +    if (memtop > BIT_ULL(pa_bits)) {
> > +       error_report("Addressing limited to %d bits, but memory exceeds it 
> > by %llu bytes\n",
> > +                    pa_bits, memtop - BIT_ULL(pa_bits));
> >          exit(EXIT_FAILURE);
> >      }
> >      if (base < device_memory_base) {
> > @@ -1711,7 +1719,13 @@ static void virt_set_memmap(VirtMachineState *vms)
> >          vms->memmap[i].size = size;
> >          base += size;
> >      }
> > -    vms->highest_gpa = (vms->highmem ? base : memtop) - 1;
> > +
> > +    /*
> > +     * If base fits within pa_bits, all good. If it doesn't, limit it
> > +     * to the end of RAM, which is guaranteed to fit within pa_bits.
> > +     */
> > +    vms->highest_gpa = (base <= BIT_ULL(pa_bits) ? base : memtop) - 1;
> > +
> >      if (device_memory_size > 0) {
> >          ms->device_memory = g_malloc0(sizeof(*ms->device_memory));
> >          ms->device_memory->base = device_memory_base;
> > @@ -1902,12 +1916,38 @@ static void machvirt_init(MachineState *machine)
> >      unsigned int smp_cpus = machine->smp.cpus;
> >      unsigned int max_cpus = machine->smp.max_cpus;
> Move the cpu_type check before?
> 
>     if (!cpu_type_valid(machine->cpu_type)) {
>         error_report("mach-virt: CPU type %s not supported",
> machine->cpu_type);
>         exit(1);
>     }
> >

Yes, very good point. I wonder why this was tucked away past
computing the memory map and the GIC configuration... Anyway, I'll
move it up.

Thanks,

        M.

-- 
Without deviation from the norm, progress is not possible.