Commit c87759ce authored by Alex Williamson's avatar Alex Williamson Committed by Paolo Bonzini
Browse files

q35: Revert to kernel irqchip 

Commit b2fc91db ("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: b2fc91db ("q35: set split kernel irqchip as default")
Signed-off-by: default avatarAlex Williamson <alex.williamson@redhat.com>
Reviewed-by: default avatarPeter Xu <peterx@redhat.com>
Message-Id: <155786484688.13873.6037015630912983760.stgit@gimli.home>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 7f27154d

hw/core/machine.c

+3 −0
Original line number Diff line number Diff line
@@ -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);

hw/i386/pc.c

+3 −0
Original line number Diff line number Diff line
@@ -110,6 +110,9 @@ 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);

hw/i386/pc_q35.c

+14 −2
Original line number Diff line number Diff line
@@ -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);

}

include/hw/boards.h

+3 −0
Original line number Diff line number Diff line
@@ -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;

include/hw/i386/pc.h

+3 −0
Original line number Diff line number Diff line
@@ -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;