Re: [Qemu-devel] [PATCH 2/2] pc: add 'etc/reserved-memory-end' fw_cfg interface for SeaBIOS

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 12 Nov 2013 19:26:02 +0100
Paolo Bonzini <pbonzini@redhat.com> wrote:

> Il 12/11/2013 14:58, Igor Mammedov ha scritto:
> > 'etc/reserved-memory-end' will allow QEMU to tell BIOS where PCI
> > BARs mapping could safely start in high memory.
> > 
> > Allowing BIOS to start mapping 64-bit PCI BARs at address where it
> > wouldn't conflict with other mappings QEMU might place before it.
> > 
> > That permits QEMU to reserve extra address space before
> > 64-bit PCI hole for memory hotplug.
> 
> I may be royally wrong, but I think the new file should only be added to
> new machine types.  Otherwise, after migrating old machine types from
> new QEMU to old QEMU, you may end up with PCI BARs mapped outside the
> "PCI windows" that exist until before patch 1/2 of this series.
> 
> Does this make sense?
it will shift BARs only when 'etc/reserved-memory-end' != above4gram_end,
presently 'etc/reserved-memory-end' == above4gram_end, so it doesn't affect
new->old or old->new migration.
Just to be sure I've done new->old and old->new migration testing, it looks
like nothing is broken by patch.

When  'etc/reserved-memory-end' > above4gram_end, new->old migration is
unlikely (unrealistically) to be broken due to default 64bit PCI hole size in
old QEMU is 1ULL << 62, so to become broken guest should have a BAR that will
go beyond 1ULL << 62 border.

But your question have reminded me to make sure that memory hotplug should be
disabled for old machine type to avoid clash of memory hotplug region and old
64-bit PCI window.

> 
> Also, would it make sense to use the e820 interface that Gerd has added,
> instead of a new fw_cfg file?
Gerd suggested it before, but we've come to agreement that dedicated file
is cleaner approach than extending standard e820 table with QEMU specific
extensions. http://www.mail-archive.com/qemu-devel@nongnu.org/msg200359.html

> 
> Thanks,
> 
> Paolo
> 
> 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> >  hw/i386/pc.c         | 14 +++++++++++++-
> >  hw/pci-host/piix.c   |  3 ++-
> >  hw/pci-host/q35.c    |  3 ++-
> >  include/hw/i386/pc.h |  3 ++-
> >  4 files changed, 19 insertions(+), 4 deletions(-)
> > 
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index 6c82ada..b504047 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -1095,11 +1095,23 @@ PcGuestInfo *pc_guest_info_init(ram_addr_t below_4g_mem_size,
> >  
> >  /* setup pci memory address space mapping into system address space */
> >  void pc_pci_as_mapping_init(Object *owner, MemoryRegion *system_memory,
> > -                            MemoryRegion *pci_address_space)
> > +                            MemoryRegion *pci_address_space,
> > +                            uint64_t reserved_memory_end)
> >  {
> > +    uint64_t *val;
> > +    FWCfgState *fw_cfg = fw_cfg_find();
> > +
> >      /* Set to lower priority than RAM */
> >      memory_region_add_subregion_overlap(system_memory, 0x0,
> >                                          pci_address_space, -1);
> > +    g_assert(fw_cfg);
> > +    /*
> > +     *  Align address at 1G, this makes sure it can be exactly covered
> > +     *  with a PAT entry even when using huge pages.
> > +     */
> > +    val = g_malloc(sizeof(*val));
> > +    *val = cpu_to_le64(ROUND_UP(reserved_memory_end, 0x1ULL << 30));
> > +    fw_cfg_add_file(fw_cfg, "etc/reserved-memory-end", val, sizeof(*val));
> >  }
> >  
> >  void pc_acpi_init(const char *default_dsdt)
> > diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
> > index 5d4e290..16205e7 100644
> > --- a/hw/pci-host/piix.c
> > +++ b/hw/pci-host/piix.c
> > @@ -351,7 +351,8 @@ PCIBus *i440fx_init(PCII440FXState **pi440fx_state,
> >  
> >      /* setup pci memory mapping */
> >      pc_pci_as_mapping_init(OBJECT(f), f->system_memory,
> > -                           f->pci_address_space);
> > +                           f->pci_address_space,
> > +                           0x100000000ULL + above_4g_mem_size);
> >  
> >      memory_region_init_alias(&f->smram_region, OBJECT(d), "smram-region",
> >                               f->pci_address_space, 0xa0000, 0x20000);
> > diff --git a/hw/pci-host/q35.c b/hw/pci-host/q35.c
> > index d1792de..1293353 100644
> > --- a/hw/pci-host/q35.c
> > +++ b/hw/pci-host/q35.c
> > @@ -353,7 +353,8 @@ static int mch_init(PCIDevice *d)
> >  
> >      /* setup pci memory mapping */
> >      pc_pci_as_mapping_init(OBJECT(mch), mch->system_memory,
> > -                           mch->pci_address_space);
> > +                           mch->pci_address_space,
> > +                           0x100000000ULL + mch->above_4g_mem_size);
> >  
> >      /* smram */
> >      cpu_smm_register(&mch_set_smm, mch);
> > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > index 8b3be3c..2663046 100644
> > --- a/include/hw/i386/pc.h
> > +++ b/include/hw/i386/pc.h
> > @@ -130,7 +130,8 @@ PcGuestInfo *pc_guest_info_init(ram_addr_t below_4g_mem_size,
> >  
> >  
> >  void pc_pci_as_mapping_init(Object *owner, MemoryRegion *system_memory,
> > -                            MemoryRegion *pci_address_space);
> > +                            MemoryRegion *pci_address_space,
> > +                            uint64_t reserved_memory_end);
> >  
> >  FWCfgState *pc_memory_init(MemoryRegion *system_memory,
> >                             const char *kernel_filename,
> > 
> 


-- 
Regards,
  Igor