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[libvirt] [PATCH] qemu: use 'bochs' video type by default for UEFI domains

Jonathon Jongsma posted 1 patch 4 years, 7 months ago
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Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/libvirt tags/patchew/20190828215239.32185-1-jjongsma@redhat.com
src/qemu/qemu_domain.c                        | 19 +++++----
src/qemu/qemu_domain.h                        |  1 +
.../video-default-nouefi.x86_64-latest.args   | 36 +++++++++++++++++
.../qemuxml2argvdata/video-default-nouefi.xml | 20 ++++++++++
.../video-default-uefi.x86_64-latest.args     | 40 +++++++++++++++++++
tests/qemuxml2argvdata/video-default-uefi.xml | 22 ++++++++++
tests/qemuxml2argvtest.c                      |  2 +
7 files changed, 133 insertions(+), 7 deletions(-)
create mode 100644 tests/qemuxml2argvdata/video-default-nouefi.x86_64-latest.args
create mode 100644 tests/qemuxml2argvdata/video-default-nouefi.xml
create mode 100644 tests/qemuxml2argvdata/video-default-uefi.x86_64-latest.args
create mode 100644 tests/qemuxml2argvdata/video-default-uefi.xml
[libvirt] [PATCH] qemu: use 'bochs' video type by default for UEFI domains
Posted by Jonathon Jongsma 4 years, 7 months ago 
The 'bochs' video device doesn't have any legacy vga emulation so the
attack surface is much lower. It works with OVMF, so UEFI guests should
not see any functional difference to VGA.

https://bugzilla.redhat.com/show_bug.cgi?id=1707119

Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
---
NOTE:
You may run into an error when trying to use the bochs video device. For
example:

    error: internal error: process exited while connecting to monitor:
    2019-08-28T21:32:20.134546Z qemu-system-x86_64: -device
    bochs-display,id=video0,vgamem=16384k,bus=pcie.0,addr=0x1: failed to find
    romfile "vgabios-bochs-display.bin"

This should be solved in e.g. Fedora 31 with newer releases of seabios/qemu. As
a temporary workaround, you can symlink the appropriate vgabios file under
/usr/share/qemu/.


 src/qemu/qemu_domain.c                        | 19 +++++----
 src/qemu/qemu_domain.h                        |  1 +
 .../video-default-nouefi.x86_64-latest.args   | 36 +++++++++++++++++
 .../qemuxml2argvdata/video-default-nouefi.xml | 20 ++++++++++
 .../video-default-uefi.x86_64-latest.args     | 40 +++++++++++++++++++
 tests/qemuxml2argvdata/video-default-uefi.xml | 22 ++++++++++
 tests/qemuxml2argvtest.c                      |  2 +
 7 files changed, 133 insertions(+), 7 deletions(-)
 create mode 100644 tests/qemuxml2argvdata/video-default-nouefi.x86_64-latest.args
 create mode 100644 tests/qemuxml2argvdata/video-default-nouefi.xml
 create mode 100644 tests/qemuxml2argvdata/video-default-uefi.x86_64-latest.args
 create mode 100644 tests/qemuxml2argvdata/video-default-uefi.xml

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 4998474dc9..7ecb89ac84 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -4584,6 +4584,14 @@ qemuDomainValidateCpuCount(const virDomainDef *def,
 }
 
 
+static bool
+qemuDomainDefIsUEFI(const virDomainDef *def)
+{
+    return ((def->os.firmware == VIR_DOMAIN_OS_DEF_FIRMWARE_EFI ||
+             (def->os.loader && def->os.loader->type ==
+              VIR_DOMAIN_LOADER_TYPE_PFLASH)));
+}
+
 static int
 qemuDomainDefValidate(const virDomainDef *def,
                       virCapsPtr caps ATTRIBUTE_UNUSED,
@@ -4606,10 +4614,7 @@ qemuDomainDefValidate(const virDomainDef *def,
     }
 
     /* On x86, UEFI requires ACPI */
-    if ((def->os.firmware == VIR_DOMAIN_OS_DEF_FIRMWARE_EFI ||
-         (def->os.loader &&
-          def->os.loader->type == VIR_DOMAIN_LOADER_TYPE_PFLASH)) &&
-        ARCH_IS_X86(def->os.arch) &&
+    if (qemuDomainDefIsUEFI(def) && ARCH_IS_X86(def->os.arch) &&
         def->features[VIR_DOMAIN_FEATURE_ACPI] != VIR_TRISTATE_SWITCH_ON) {
         virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
                        _("UEFI requires ACPI on this architecture"));
@@ -4619,9 +4624,7 @@ qemuDomainDefValidate(const virDomainDef *def,
     /* On aarch64, ACPI requires UEFI */
     if (def->features[VIR_DOMAIN_FEATURE_ACPI] == VIR_TRISTATE_SWITCH_ON &&
         def->os.arch == VIR_ARCH_AARCH64 &&
-        (def->os.firmware != VIR_DOMAIN_OS_DEF_FIRMWARE_EFI &&
-         (!def->os.loader ||
-          def->os.loader->type != VIR_DOMAIN_LOADER_TYPE_PFLASH))) {
+        !qemuDomainDefIsUEFI(def)) {
         virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
                        _("ACPI requires UEFI on this architecture"));
         goto cleanup;
@@ -7452,6 +7455,8 @@ qemuDomainDeviceVideoDefPostParse(virDomainVideoDefPtr video,
                  qemuDomainIsRISCVVirt(def) ||
                  ARCH_IS_S390(def->os.arch))
             video->type = VIR_DOMAIN_VIDEO_TYPE_VIRTIO;
+        else if (qemuDomainDefIsUEFI(def))
+            video->type = VIR_DOMAIN_VIDEO_TYPE_BOCHS;
         else
             video->type = VIR_DOMAIN_VIDEO_TYPE_CIRRUS;
     }
diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
index 37a00323a7..c6deab1c52 100644
--- a/src/qemu/qemu_domain.h
+++ b/src/qemu/qemu_domain.h
@@ -923,6 +923,7 @@ bool qemuDomainHasBuiltinIDE(const virDomainDef *def);
 bool qemuDomainNeedsFDC(const virDomainDef *def);
 bool qemuDomainSupportsPCI(virDomainDefPtr def,
                            virQEMUCapsPtr qemuCaps);
+bool qemuDomainIsUEFI(const virDomainDef *def);
 
 void qemuDomainUpdateCurrentMemorySize(virDomainObjPtr vm);
 
diff --git a/tests/qemuxml2argvdata/video-default-nouefi.x86_64-latest.args b/tests/qemuxml2argvdata/video-default-nouefi.x86_64-latest.args
new file mode 100644
index 0000000000..f0c9e36594
--- /dev/null
+++ b/tests/qemuxml2argvdata/video-default-nouefi.x86_64-latest.args
@@ -0,0 +1,36 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/tmp/lib/domain--1-guest \
+USER=test \
+LOGNAME=test \
+XDG_DATA_HOME=/tmp/lib/domain--1-guest/.local/share \
+XDG_CACHE_HOME=/tmp/lib/domain--1-guest/.cache \
+XDG_CONFIG_HOME=/tmp/lib/domain--1-guest/.config \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-x86_64 \
+-name guest=guest,debug-threads=on \
+-S \
+-object secret,id=masterKey0,format=raw,\
+file=/tmp/lib/domain--1-guest/master-key.aes \
+-machine q35,accel=tcg,usb=off,dump-guest-core=off \
+-cpu Haswell \
+-m 1024 \
+-overcommit mem-lock=off \
+-smp 1,sockets=1,cores=1,threads=1 \
+-uuid 26b73eb7-f8c4-4541-ae6f-06607a1b21c3 \
+-display none \
+-no-user-config \
+-nodefaults \
+-chardev socket,id=charmonitor,fd=1729,server,nowait \
+-mon chardev=charmonitor,id=monitor,mode=control \
+-rtc base=utc \
+-no-shutdown \
+-boot strict=on \
+-device pcie-root-port,port=0x10,chassis=1,id=pci.1,bus=pcie.0,\
+multifunction=on,addr=0x2 \
+-device pcie-root-port,port=0x11,chassis=2,id=pci.2,bus=pcie.0,addr=0x2.0x1 \
+-device qemu-xhci,id=usb,bus=pci.1,addr=0x0 \
+-device cirrus-vga,id=video0,bus=pcie.0,addr=0x1 \
+-sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,\
+resourcecontrol=deny \
+-msg timestamp=on
diff --git a/tests/qemuxml2argvdata/video-default-nouefi.xml b/tests/qemuxml2argvdata/video-default-nouefi.xml
new file mode 100644
index 0000000000..7db2bedf6c
--- /dev/null
+++ b/tests/qemuxml2argvdata/video-default-nouefi.xml
@@ -0,0 +1,20 @@
+<domain type='qemu'>
+  <name>guest</name>
+  <uuid>26b73eb7-f8c4-4541-ae6f-06607a1b21c3</uuid>
+  <memory unit='KiB'>1048576</memory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='q35'>hvm</type>
+  </os>
+  <features>
+    <acpi/>
+  </features>
+  <cpu mode='custom'>
+    <model>Haswell</model>
+  </cpu>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <memballoon model='none'/>
+    <video/>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvdata/video-default-uefi.x86_64-latest.args b/tests/qemuxml2argvdata/video-default-uefi.x86_64-latest.args
new file mode 100644
index 0000000000..75c599f321
--- /dev/null
+++ b/tests/qemuxml2argvdata/video-default-uefi.x86_64-latest.args
@@ -0,0 +1,40 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/tmp/lib/domain--1-guest \
+USER=test \
+LOGNAME=test \
+XDG_DATA_HOME=/tmp/lib/domain--1-guest/.local/share \
+XDG_CACHE_HOME=/tmp/lib/domain--1-guest/.cache \
+XDG_CONFIG_HOME=/tmp/lib/domain--1-guest/.config \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-x86_64 \
+-name guest=guest,debug-threads=on \
+-S \
+-object secret,id=masterKey0,format=raw,\
+file=/tmp/lib/domain--1-guest/master-key.aes \
+-machine q35,accel=tcg,usb=off,dump-guest-core=off \
+-cpu Haswell \
+-drive file=/usr/share/OVMF/OVMF_CODE.fd,if=pflash,format=raw,unit=0,\
+readonly=on \
+-drive file=/var/lib/libvirt/qemu/nvram/guest_VARS.fd,if=pflash,format=raw,\
+unit=1 \
+-m 1024 \
+-overcommit mem-lock=off \
+-smp 1,sockets=1,cores=1,threads=1 \
+-uuid 26b73eb7-f8c4-4541-ae6f-06607a1b21c3 \
+-display none \
+-no-user-config \
+-nodefaults \
+-chardev socket,id=charmonitor,fd=1729,server,nowait \
+-mon chardev=charmonitor,id=monitor,mode=control \
+-rtc base=utc \
+-no-shutdown \
+-boot strict=on \
+-device pcie-root-port,port=0x10,chassis=1,id=pci.1,bus=pcie.0,\
+multifunction=on,addr=0x2 \
+-device pcie-root-port,port=0x11,chassis=2,id=pci.2,bus=pcie.0,addr=0x2.0x1 \
+-device qemu-xhci,id=usb,bus=pci.1,addr=0x0 \
+-device bochs-display,id=video0,vgamem=16384k,bus=pcie.0,addr=0x1 \
+-sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,\
+resourcecontrol=deny \
+-msg timestamp=on
diff --git a/tests/qemuxml2argvdata/video-default-uefi.xml b/tests/qemuxml2argvdata/video-default-uefi.xml
new file mode 100644
index 0000000000..59e880c78c
--- /dev/null
+++ b/tests/qemuxml2argvdata/video-default-uefi.xml
@@ -0,0 +1,22 @@
+<domain type='qemu'>
+  <name>guest</name>
+  <uuid>26b73eb7-f8c4-4541-ae6f-06607a1b21c3</uuid>
+  <memory unit='KiB'>1048576</memory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='q35'>hvm</type>
+    <loader readonly='yes' type='pflash'>/usr/share/OVMF/OVMF_CODE.fd</loader>
+    <nvram>/var/lib/libvirt/qemu/nvram/guest_VARS.fd</nvram>
+  </os>
+  <features>
+    <acpi/>
+  </features>
+  <cpu mode='custom'>
+    <model>Haswell</model>
+  </cpu>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <memballoon model='none'/>
+    <video/>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 9395cc19a2..671e79e631 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -2045,6 +2045,8 @@ mymain(void)
     DO_TEST("video-none-device",
             QEMU_CAPS_VNC);
     DO_TEST_PARSE_ERROR("video-invalid-multiple-devices", NONE);
+    DO_TEST_CAPS_LATEST("video-default-uefi");
+    DO_TEST_CAPS_LATEST("video-default-nouefi");
 
     DO_TEST("virtio-rng-default",
             QEMU_CAPS_DEVICE_VIRTIO_RNG,
-- 
2.21.0

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Re: [libvirt] [PATCH] qemu: use 'bochs' video type by default for UEFI domains
Posted by Peter Krempa 4 years, 7 months ago 
On Wed, Aug 28, 2019 at 16:52:39 -0500, Jonathon Jongsma wrote:
> The 'bochs' video device doesn't have any legacy vga emulation so the
> attack surface is much lower. It works with OVMF, so UEFI guests should
> not see any functional difference to VGA.
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=1707119
> 
> Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
> ---

Historically we did not allow change of behaviour when filling in
defaults unless the old configuration stopped to be supported by qemu
and we could detect it. I don't thik this case can be excused.

> NOTE:
> You may run into an error when trying to use the bochs video device. For
> example:
> 
>     error: internal error: process exited while connecting to monitor:
>     2019-08-28T21:32:20.134546Z qemu-system-x86_64: -device
>     bochs-display,id=video0,vgamem=16384k,bus=pcie.0,addr=0x1: failed to find
>     romfile "vgabios-bochs-display.bin"
> 
> This should be solved in e.g. Fedora 31 with newer releases of seabios/qemu. As
> a temporary workaround, you can symlink the appropriate vgabios file under
> /usr/share/qemu/.

Similarly I don't think this is acceptable.

>  src/qemu/qemu_domain.c                        | 19 +++++----
>  src/qemu/qemu_domain.h                        |  1 +
>  .../video-default-nouefi.x86_64-latest.args   | 36 +++++++++++++++++
>  .../qemuxml2argvdata/video-default-nouefi.xml | 20 ++++++++++
>  .../video-default-uefi.x86_64-latest.args     | 40 +++++++++++++++++++
>  tests/qemuxml2argvdata/video-default-uefi.xml | 22 ++++++++++
>  tests/qemuxml2argvtest.c                      |  2 +
>  7 files changed, 133 insertions(+), 7 deletions(-)
>  create mode 100644 tests/qemuxml2argvdata/video-default-nouefi.x86_64-latest.args
>  create mode 100644 tests/qemuxml2argvdata/video-default-nouefi.xml
>  create mode 100644 tests/qemuxml2argvdata/video-default-uefi.x86_64-latest.args
>  create mode 100644 tests/qemuxml2argvdata/video-default-uefi.xml
> 
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index 4998474dc9..7ecb89ac84 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -4584,6 +4584,14 @@ qemuDomainValidateCpuCount(const virDomainDef *def,
>  }
>  
>  
> +static bool
> +qemuDomainDefIsUEFI(const virDomainDef *def)
> +{
> +    return ((def->os.firmware == VIR_DOMAIN_OS_DEF_FIRMWARE_EFI ||
> +             (def->os.loader && def->os.loader->type ==
> +              VIR_DOMAIN_LOADER_TYPE_PFLASH)));
> +}
> +
>  static int
>  qemuDomainDefValidate(const virDomainDef *def,
>                        virCapsPtr caps ATTRIBUTE_UNUSED,
> @@ -4606,10 +4614,7 @@ qemuDomainDefValidate(const virDomainDef *def,
>      }
>  
>      /* On x86, UEFI requires ACPI */
> -    if ((def->os.firmware == VIR_DOMAIN_OS_DEF_FIRMWARE_EFI ||
> -         (def->os.loader &&
> -          def->os.loader->type == VIR_DOMAIN_LOADER_TYPE_PFLASH)) &&
> -        ARCH_IS_X86(def->os.arch) &&
> +    if (qemuDomainDefIsUEFI(def) && ARCH_IS_X86(def->os.arch) &&
>          def->features[VIR_DOMAIN_FEATURE_ACPI] != VIR_TRISTATE_SWITCH_ON) {
>          virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
>                         _("UEFI requires ACPI on this architecture"));
> @@ -4619,9 +4624,7 @@ qemuDomainDefValidate(const virDomainDef *def,
>      /* On aarch64, ACPI requires UEFI */
>      if (def->features[VIR_DOMAIN_FEATURE_ACPI] == VIR_TRISTATE_SWITCH_ON &&
>          def->os.arch == VIR_ARCH_AARCH64 &&
> -        (def->os.firmware != VIR_DOMAIN_OS_DEF_FIRMWARE_EFI &&
> -         (!def->os.loader ||
> -          def->os.loader->type != VIR_DOMAIN_LOADER_TYPE_PFLASH))) {
> +        !qemuDomainDefIsUEFI(def)) {
>          virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
>                         _("ACPI requires UEFI on this architecture"));
>          goto cleanup;

The three hunks above are refactors not functionally connected with the
behaviour change later, thus they should be in a separate patch.


> @@ -7452,6 +7455,8 @@ qemuDomainDeviceVideoDefPostParse(virDomainVideoDefPtr video,
>                   qemuDomainIsRISCVVirt(def) ||
>                   ARCH_IS_S390(def->os.arch))
>              video->type = VIR_DOMAIN_VIDEO_TYPE_VIRTIO;
> +        else if (qemuDomainDefIsUEFI(def))
> +            video->type = VIR_DOMAIN_VIDEO_TYPE_BOCHS;

'bochs-display' seems to be supported starting qemu 3.0.0, but
pflash/ovmf starting qemu 1.7, so this can result in invalid
configuration for older qemu versions.

>          else
>              video->type = VIR_DOMAIN_VIDEO_TYPE_CIRRUS;
>      }
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Re: [libvirt] [PATCH] qemu: use 'bochs' video type by default for UEFI domains
Posted by Daniel P. Berrangé 4 years, 7 months ago 
On Thu, Aug 29, 2019 at 08:22:55AM +0200, Peter Krempa wrote:
> On Wed, Aug 28, 2019 at 16:52:39 -0500, Jonathon Jongsma wrote:
> > The 'bochs' video device doesn't have any legacy vga emulation so the
> > attack surface is much lower. It works with OVMF, so UEFI guests should
> > not see any functional difference to VGA.
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=1707119
> > 
> > Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
> > ---
> 
> Historically we did not allow change of behaviour when filling in
> defaults unless the old configuration stopped to be supported by qemu
> and we could detect it. I don't thik this case can be excused.

Yep, we can't do this, and in any case modern guests should likely
be given virtio-vga instead, which can be decided via libosinfo
rules.



Regards,
Daniel
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Re: [libvirt] [PATCH] qemu: use 'bochs' video type by default for UEFI domains
Posted by Andrea Bolognani 4 years, 7 months ago 
On Thu, 2019-08-29 at 08:22 +0200, Peter Krempa wrote:
> On Wed, Aug 28, 2019 at 16:52:39 -0500, Jonathon Jongsma wrote:
> > @@ -7452,6 +7455,8 @@ qemuDomainDeviceVideoDefPostParse(virDomainVideoDefPtr video,
> >                   qemuDomainIsRISCVVirt(def) ||
> >                   ARCH_IS_S390(def->os.arch))
> >              video->type = VIR_DOMAIN_VIDEO_TYPE_VIRTIO;
> > +        else if (qemuDomainDefIsUEFI(def))
> > +            video->type = VIR_DOMAIN_VIDEO_TYPE_BOCHS;
> 
> 'bochs-display' seems to be supported starting qemu 3.0.0, but
> pflash/ovmf starting qemu 1.7, so this can result in invalid
> configuration for older qemu versions.

Agreed, we can't just change the default like this.

If we want new guests to use bochs-display, then that needs to be
wired up in virt-manager in a way that's conditional to support being
available both on the host and in the guest.

Incidentally, and I haven't followed this closely so apologies if I'm
asking a silly question, if the point of bochs-display is to have a
video device without legacy VGA emulation then why aren't we using
the existing virtio-gpu, which has been around a lot longer and has
better support throughout the stack, instead?

Please by all means *do* send the patch introducing
qemuDomainDefIsUEFI() separately, it's a pretty nice cleanup.

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Re: [libvirt] [PATCH] qemu: use 'bochs' video type by default for UEFI domains
Posted by Gerd Hoffmann 4 years, 7 months ago 
  Hi,

> Incidentally, and I haven't followed this closely so apologies if I'm
> asking a silly question, if the point of bochs-display is to have a
> video device without legacy VGA emulation then why aren't we using
> the existing virtio-gpu, which has been around a lot longer and has
> better support throughout the stack, instead?

Well, virtio-gpu (on x86) actually is "-device virtio-vga".  That comes
with legacy VGA emulation, for the boot display ...

For UEFI guests with virtio-gpu support it is possible to use "-display
virtio-gpu-pci" instead (simliar to arm).  Only drawback is that you
can't have a EFI GOB with virtio-gpu-pci, so efifb doesn't work.  Linux
kernel console shows up after the virtio-gpu driver loads, which is
rather late compared to efifb.

For UEFI guests without virtio-gpu support "-device virtio-gpu-pci" will
not work due to the lack of EFI GOB support.  For these guests
"-display bochs-display" should preferred over "-device VGA", to get rid
of the unused legacy VGA emulation (and thereby reduce the attack
surface).

Also note that bochs-display can be plugged into pcie slots (that is
true for virtio-gpu-pci too btw).

Not sure whenever implementing this works better in libvirt or
libosinfo.

cheers,
  Gerd

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Re: [libvirt] [PATCH] qemu: use 'bochs' video type by default for UEFI domains
Posted by Daniel P. Berrangé 4 years, 7 months ago 
On Thu, Aug 29, 2019 at 12:19:49PM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> > Incidentally, and I haven't followed this closely so apologies if I'm
> > asking a silly question, if the point of bochs-display is to have a
> > video device without legacy VGA emulation then why aren't we using
> > the existing virtio-gpu, which has been around a lot longer and has
> > better support throughout the stack, instead?
> 
> Well, virtio-gpu (on x86) actually is "-device virtio-vga".  That comes
> with legacy VGA emulation, for the boot display ...
> 
> For UEFI guests with virtio-gpu support it is possible to use "-display
> virtio-gpu-pci" instead (simliar to arm).  Only drawback is that you
> can't have a EFI GOB with virtio-gpu-pci, so efifb doesn't work.  Linux
> kernel console shows up after the virtio-gpu driver loads, which is
> rather late compared to efifb.
> 
> For UEFI guests without virtio-gpu support "-device virtio-gpu-pci" will
> not work due to the lack of EFI GOB support.  For these guests
> "-display bochs-display" should preferred over "-device VGA", to get rid
> of the unused legacy VGA emulation (and thereby reduce the attack
> surface).
> 
> Also note that bochs-display can be plugged into pcie slots (that is
> true for virtio-gpu-pci too btw).

BTW a while ago you did a really helpful blog post describing best usage
for each display type

  https://www.kraxel.org/blog/2014/10/qemu-using-cirrus-considered-harmful/

there's been quite a few changes since then with virtio-vga and bochs-display
arriving, so it would be awesome if you wrote an updated blog post, or even
added something to the main qemu-doc.texi doc giving recommandations for what
to use for guests. 


Regards,
Daniel
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Re: [libvirt] [PATCH] qemu: use 'bochs' video type by default for UEFI domains
Posted by Fabiano Fidêncio 4 years, 7 months ago 
On Thu, Aug 29, 2019 at 12:21 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
>
>   Hi,
>
> > Incidentally, and I haven't followed this closely so apologies if I'm
> > asking a silly question, if the point of bochs-display is to have a
> > video device without legacy VGA emulation then why aren't we using
> > the existing virtio-gpu, which has been around a lot longer and has
> > better support throughout the stack, instead?
>
> Well, virtio-gpu (on x86) actually is "-device virtio-vga".  That comes
> with legacy VGA emulation, for the boot display ...
>
> For UEFI guests with virtio-gpu support it is possible to use "-display
> virtio-gpu-pci" instead (simliar to arm).  Only drawback is that you
> can't have a EFI GOB with virtio-gpu-pci, so efifb doesn't work.  Linux
> kernel console shows up after the virtio-gpu driver loads, which is
> rather late compared to efifb.
>
> For UEFI guests without virtio-gpu support "-device virtio-gpu-pci" will
> not work due to the lack of EFI GOB support.  For these guests
> "-display bochs-display" should preferred over "-device VGA", to get rid
> of the unused legacy VGA emulation (and thereby reduce the attack
> surface).
>
> Also note that bochs-display can be plugged into pcie slots (that is
> true for virtio-gpu-pci too btw).
>
> Not sure whenever implementing this works better in libvirt or
> libosinfo.

I do believe this piece should go to libosinfo.
However, the decision of what exactly to use due to lack of this or
that device, should be done in the management apps, in a similar way
of what was done for the q35 work.

>
> cheers,
>   Gerd
>
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