On Tue, May 14, 2019 at 02:14:41PM -0600, Alex Williamson wrote: > Commit b2fc91db8447 ("q35: set split kernel irqchip as default") changed > the default for the pc-q35-4.0 machine type to use split irqchip, which > turned out to have disasterous effects on vfio-pci INTx support. KVM > resampling irqfds are registered for handling these interrupts, but > these are non-functional in split irqchip mode. We can't simply test > for split irqchip in QEMU as userspace handling of this interrupt is a > significant performance regression versus KVM handling (GeForce GPUs > assigned to Windows VMs are non-functional without forcing MSI mode or > re-enabling kernel irqchip). > > The resolution is to revert the change in default irqchip mode in the > pc-q35-4.1 machine and create a pc-q35-4.0.1 machine for the 4.0-stable > branch. The qemu-q35-4.0 machine type should not be used in vfio-pci > configurations for devices requiring legacy INTx support without > explicitly modifying the VM configuration to use kernel irqchip. > > Link: https://bugs.launchpad.net/qemu/+bug/1826422 > Fixes: b2fc91db8447 ("q35: set split kernel irqchip as default") > Signed-off-by: Alex Williamson <alex.william...@redhat.com>
OK I guess but it's really a kvm patch. So I'd like Paolo to review and merge if appropriate. Can't say this makes me too happy. split irqchip has a bunch of advantages. > --- > hw/core/machine.c | 3 +++ > hw/i386/pc.c | 3 +++ > hw/i386/pc_q35.c | 16 ++++++++++++++-- > include/hw/boards.h | 3 +++ > include/hw/i386/pc.h | 3 +++ > 5 files changed, 26 insertions(+), 2 deletions(-) > > diff --git a/hw/core/machine.c b/hw/core/machine.c > index 5d046a43e3d2..e41e6698ac9f 100644 > --- a/hw/core/machine.c > +++ b/hw/core/machine.c > @@ -24,6 +24,9 @@ > #include "hw/pci/pci.h" > #include "hw/mem/nvdimm.h" > > +GlobalProperty hw_compat_4_0_1[] = {}; > +const size_t hw_compat_4_0_1_len = G_N_ELEMENTS(hw_compat_4_0_1); > + > GlobalProperty hw_compat_4_0[] = {}; > const size_t hw_compat_4_0_len = G_N_ELEMENTS(hw_compat_4_0); > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index d98b737b8f3b..b5311e7e2bd5 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -115,6 +115,9 @@ struct hpet_fw_config hpet_cfg = {.count = UINT8_MAX}; > /* Physical Address of PVH entry point read from kernel ELF NOTE */ > static size_t pvh_start_addr; > > +GlobalProperty pc_compat_4_0_1[] = {}; > +const size_t pc_compat_4_0_1_len = G_N_ELEMENTS(pc_compat_4_0_1); > + > GlobalProperty pc_compat_4_0[] = {}; > const size_t pc_compat_4_0_len = G_N_ELEMENTS(pc_compat_4_0); > > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c > index 37dd350511a9..dcddc6466200 100644 > --- a/hw/i386/pc_q35.c > +++ b/hw/i386/pc_q35.c > @@ -357,7 +357,7 @@ static void pc_q35_machine_options(MachineClass *m) > m->units_per_default_bus = 1; > m->default_machine_opts = "firmware=bios-256k.bin"; > m->default_display = "std"; > - m->default_kernel_irqchip_split = true; > + m->default_kernel_irqchip_split = false; > m->no_floppy = 1; > machine_class_allow_dynamic_sysbus_dev(m, TYPE_AMD_IOMMU_DEVICE); > machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_DEVICE); > @@ -374,10 +374,22 @@ static void pc_q35_4_1_machine_options(MachineClass *m) > DEFINE_Q35_MACHINE(v4_1, "pc-q35-4.1", NULL, > pc_q35_4_1_machine_options); > > -static void pc_q35_4_0_machine_options(MachineClass *m) > +static void pc_q35_4_0_1_machine_options(MachineClass *m) > { > pc_q35_4_1_machine_options(m); > m->alias = NULL; > + compat_props_add(m->compat_props, hw_compat_4_0_1, hw_compat_4_0_1_len); > + compat_props_add(m->compat_props, pc_compat_4_0_1, pc_compat_4_0_1_len); > +} > + > +DEFINE_Q35_MACHINE(v4_0_1, "pc-q35-4.0.1", NULL, > + pc_q35_4_0_1_machine_options); > + > +static void pc_q35_4_0_machine_options(MachineClass *m) > +{ > + pc_q35_4_0_1_machine_options(m); > + m->default_kernel_irqchip_split = true; > + m->alias = NULL; > compat_props_add(m->compat_props, hw_compat_4_0, hw_compat_4_0_len); > compat_props_add(m->compat_props, pc_compat_4_0, pc_compat_4_0_len); > } > diff --git a/include/hw/boards.h b/include/hw/boards.h > index 6f7916f88f02..6ff02bf3e472 100644 > --- a/include/hw/boards.h > +++ b/include/hw/boards.h > @@ -292,6 +292,9 @@ struct MachineState { > } \ > type_init(machine_initfn##_register_types) > > +extern GlobalProperty hw_compat_4_0_1[]; > +extern const size_t hw_compat_4_0_1_len; > + > extern GlobalProperty hw_compat_4_0[]; > extern const size_t hw_compat_4_0_len; > > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h > index 43df7230a22b..5d5636241e34 100644 > --- a/include/hw/i386/pc.h > +++ b/include/hw/i386/pc.h > @@ -293,6 +293,9 @@ int e820_add_entry(uint64_t, uint64_t, uint32_t); > int e820_get_num_entries(void); > bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *); > > +extern GlobalProperty pc_compat_4_0_1[]; > +extern const size_t pc_compat_4_0_1_len; > + > extern GlobalProperty pc_compat_4_0[]; > extern const size_t pc_compat_4_0_len; >