On Wed, Jan 10, 2018 at 12:41:52PM +0100, Igor Mammedov wrote: > On Wed, 10 Jan 2018 13:29:09 +0200 > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > On Wed, Jan 10, 2018 at 12:25:34PM +0100, Igor Mammedov wrote: > > > On Tue, 9 Jan 2018 15:58:11 +0200 > > > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > > > > > We prefer not changing table sizes depending on parameters, > > > > that's why we create a dummy table rather than just drop > > > > the MCFG table. > > > > > > > > However, a table named "QEMU" could be put to a better > > > > use than just a stub, e.g. we could use it to pass > > > > some QEMU specific info to guests. > > > > > > > > Replace with an SSDT and pad with the Nop opcode > > > > to preserve the length. > > > Not sure it's useful, do you have patches on top of that, which will use > > > this? > > > > Yes but not me - Stefan (Cc'd) wants to add a custom table. > Re-purposing dummy table that might become not dummy doesn't look like good > approach. > What if later the guest enables MCFG and reboots, DUMMY SSDT would be > replaced by MCFG?
So what's the issue? Why is this worse than a dummy QEMU table? There's actually no re-purposing here at all. Either we create an MCFG or an SSDT. We never re-purpose. > It'd be cleaner if Stefan would just use his own dedicated SSDT. SSDT doesn't always work. A data table is needed so e.g. seabios can process it easily. > > > > > > > Signed-off-by: Michael S. Tsirkin <m...@redhat.com> > > > > --- > > > > hw/i386/acpi-build.c | 17 ++++++++++++----- > > > > 1 file changed, 12 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c > > > > index 73519ab..d0afb31e 100644 > > > > --- a/hw/i386/acpi-build.c > > > > +++ b/hw/i386/acpi-build.c > > > > @@ -2419,6 +2419,8 @@ build_mcfg_q35(GArray *table_data, BIOSLinker > > > > *linker, AcpiMcfgInfo *info) > > > > { > > > > AcpiTableMcfg *mcfg; > > > > const char *sig; > > > > + const char *oem; > > > > + const char *oem_id; > > > > int len = sizeof(*mcfg) + 1 * sizeof(mcfg->allocation[0]); > > > > > > > > mcfg = acpi_data_push(table_data, len); > > > > @@ -2431,16 +2433,21 @@ build_mcfg_q35(GArray *table_data, BIOSLinker > > > > *linker, AcpiMcfgInfo *info) > > > > /* MCFG is used for ECAM which can be enabled or disabled by guest. > > > > * To avoid table size changes (which create migration issues), > > > > * always create the table even if there are no allocations, > > > > - * but set the signature to a reserved value in this case. > > > > - * ACPI spec requires OSPMs to ignore such tables. > > > > + * but fill it with Noop values. > > > > + * OSPMs ignore such tables. > > > > */ > > > > if (info->mcfg_base == PCIE_BASE_ADDR_UNMAPPED) { > > > > - /* Reserved signature: ignored by OSPM */ > > > > - sig = "QEMU"; > > > > + sig = "SSDT"; > > > > + oem = "QEMU "; > > > > + oem_id = "NOOP"; > > > > + /* 0xa3 - NoopOp */ > > > > + memset(&mcfg->reserved, 0xa3, len - offsetof(AcpiTableMcfg, > > > > reserved)); > > > > } else { > > > > sig = "MCFG"; > > > > + oem = NULL; > > > > + oem_id = NULL; > > > > } > > > > - build_header(linker, table_data, (void *)mcfg, sig, len, 1, NULL, > > > > NULL); > > > > + build_header(linker, table_data, (void *)mcfg, sig, len, 1, oem, > > > > oem_id); > > > > } > > > > > > > > /*