diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/about/build-platforms.rst | 3 | ||||
| -rw-r--r-- | docs/about/deprecated.rst | 20 | ||||
| -rw-r--r-- | docs/config/mach-virt-graphical.cfg | 4 | ||||
| -rw-r--r-- | docs/config/mach-virt-serial.cfg | 4 | ||||
| -rw-r--r-- | docs/config/q35-emulated.cfg | 2 | ||||
| -rw-r--r-- | docs/config/q35-virtio-graphical.cfg | 2 | ||||
| -rw-r--r-- | docs/config/q35-virtio-serial.cfg | 2 | ||||
| -rw-r--r-- | docs/devel/atomics.rst | 26 | ||||
| -rw-r--r-- | docs/system/i386/xen.rst | 30 | ||||
| -rw-r--r-- | docs/system/target-mips.rst | 14 |
10 files changed, 78 insertions, 29 deletions
diff --git a/docs/about/build-platforms.rst b/docs/about/build-platforms.rst index 20b97c3310..89cae5a6bb 100644 --- a/docs/about/build-platforms.rst +++ b/docs/about/build-platforms.rst @@ -67,7 +67,8 @@ Non-supported architectures may be removed in the future following the Linux OS, macOS, FreeBSD, NetBSD, OpenBSD ----------------------------------------- -The project aims to support the most recent major version at all times. Support +The project aims to support the most recent major version at all times for +up to five years after its initial release. Support for the previous major version will be dropped 2 years after the new major version is released or when the vendor itself drops support, whichever comes first. In this context, third-party efforts to extend the lifetime of a distro diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst index 15084f7bea..33b942283f 100644 --- a/docs/about/deprecated.rst +++ b/docs/about/deprecated.rst @@ -196,6 +196,26 @@ CI coverage support may bitrot away before the deprecation process completes. The little endian variants of MIPS (both 32 and 64 bit) are still a supported host architecture. +System emulation on 32-bit x86 hosts (since 8.0) +'''''''''''''''''''''''''''''''''''''''''''''''' + +Support for 32-bit x86 host deployments is increasingly uncommon in mainstream +OS distributions given the widespread availability of 64-bit x86 hardware. +The QEMU project no longer considers 32-bit x86 support for system emulation to +be an effective use of its limited resources, and thus intends to discontinue +it. Since all recent x86 hardware from the past >10 years is capable of the +64-bit x86 extensions, a corresponding 64-bit OS should be used instead. + +System emulation on 32-bit arm hosts (since 8.0) +'''''''''''''''''''''''''''''''''''''''''''''''' + +Since QEMU needs a strong host machine for running full system emulation, and +all recent powerful arm hosts support 64-bit, the QEMU project deprecates the +support for running any system emulation on 32-bit arm hosts in general. Use +64-bit arm hosts for system emulation instead. (Note: "user" mode emulation +continues to be supported on 32-bit arm hosts, too) + + QEMU API (QAPI) events ---------------------- diff --git a/docs/config/mach-virt-graphical.cfg b/docs/config/mach-virt-graphical.cfg index d6d31b17f5..eba76eb198 100644 --- a/docs/config/mach-virt-graphical.cfg +++ b/docs/config/mach-virt-graphical.cfg @@ -56,9 +56,11 @@ [machine] type = "virt" - accel = "kvm" gic-version = "host" +[accel] + accel = "kvm" + [memory] size = "1024" diff --git a/docs/config/mach-virt-serial.cfg b/docs/config/mach-virt-serial.cfg index 18a7c83731..324b0542ff 100644 --- a/docs/config/mach-virt-serial.cfg +++ b/docs/config/mach-virt-serial.cfg @@ -62,9 +62,11 @@ [machine] type = "virt" - accel = "kvm" gic-version = "host" +[accel] + accel = "kvm" + [memory] size = "1024" diff --git a/docs/config/q35-emulated.cfg b/docs/config/q35-emulated.cfg index 99ac918e78..c8806e6d36 100644 --- a/docs/config/q35-emulated.cfg +++ b/docs/config/q35-emulated.cfg @@ -61,6 +61,8 @@ [machine] type = "q35" + +[accel] accel = "kvm" [memory] diff --git a/docs/config/q35-virtio-graphical.cfg b/docs/config/q35-virtio-graphical.cfg index 4207f11e4f..148b5d2c5e 100644 --- a/docs/config/q35-virtio-graphical.cfg +++ b/docs/config/q35-virtio-graphical.cfg @@ -55,6 +55,8 @@ [machine] type = "q35" + +[accel] accel = "kvm" [memory] diff --git a/docs/config/q35-virtio-serial.cfg b/docs/config/q35-virtio-serial.cfg index d2830aec5e..023291390e 100644 --- a/docs/config/q35-virtio-serial.cfg +++ b/docs/config/q35-virtio-serial.cfg @@ -60,6 +60,8 @@ [machine] type = "q35" + +[accel] accel = "kvm" [memory] diff --git a/docs/devel/atomics.rst b/docs/devel/atomics.rst index 7957310071..633df65a97 100644 --- a/docs/devel/atomics.rst +++ b/docs/devel/atomics.rst @@ -27,7 +27,8 @@ provides macros that fall in three camps: - weak atomic access and manual memory barriers: ``qatomic_read()``, ``qatomic_set()``, ``smp_rmb()``, ``smp_wmb()``, ``smp_mb()``, - ``smp_mb_acquire()``, ``smp_mb_release()``, ``smp_read_barrier_depends()``; + ``smp_mb_acquire()``, ``smp_mb_release()``, ``smp_read_barrier_depends()``, + ``smp_mb__before_rmw()``, ``smp_mb__after_rmw()``; - sequentially consistent atomic access: everything else. @@ -472,7 +473,7 @@ and memory barriers, and the equivalents in QEMU: sequential consistency. - in QEMU, ``qatomic_read()`` and ``qatomic_set()`` do not participate in - the total ordering enforced by sequentially-consistent operations. + the ordering enforced by read-modify-write operations. This is because QEMU uses the C11 memory model. The following example is correct in Linux but not in QEMU: @@ -488,9 +489,24 @@ and memory barriers, and the equivalents in QEMU: because the read of ``y`` can be moved (by either the processor or the compiler) before the write of ``x``. - Fixing this requires an ``smp_mb()`` memory barrier between the write - of ``x`` and the read of ``y``. In the common case where only one thread - writes ``x``, it is also possible to write it like this: + Fixing this requires a full memory barrier between the write of ``x`` and + the read of ``y``. QEMU provides ``smp_mb__before_rmw()`` and + ``smp_mb__after_rmw()``; they act both as an optimization, + avoiding the memory barrier on processors where it is unnecessary, + and as a clarification of this corner case of the C11 memory model: + + +--------------------------------+ + | QEMU (correct) | + +================================+ + | :: | + | | + | a = qatomic_fetch_add(&x, 2);| + | smp_mb__after_rmw(); | + | b = qatomic_read(&y); | + +--------------------------------+ + + In the common case where only one thread writes ``x``, it is also possible + to write it like this: +--------------------------------+ | QEMU (correct) | diff --git a/docs/system/i386/xen.rst b/docs/system/i386/xen.rst index a00523b492..f06765e88c 100644 --- a/docs/system/i386/xen.rst +++ b/docs/system/i386/xen.rst @@ -9,6 +9,8 @@ KVM has support for hosting Xen guests, intercepting Xen hypercalls and event channel (Xen PV interrupt) delivery. This allows guests which expect to be run under Xen to be hosted in QEMU under Linux/KVM instead. +Using the split irqchip is mandatory for Xen support. + Setup ----- @@ -17,14 +19,14 @@ accelerator, for example for Xen 4.10: .. parsed-literal:: - |qemu_system| --accel kvm,xen-version=0x4000a + |qemu_system| --accel kvm,xen-version=0x4000a,kernel-irqchip=split Additionally, virtual APIC support can be advertised to the guest through the ``xen-vapic`` CPU flag: .. parsed-literal:: - |qemu_system| --accel kvm,xen-version=0x4000a --cpu host,+xen_vapic + |qemu_system| --accel kvm,xen-version=0x4000a,kernel-irqchip=split --cpu host,+xen_vapic When Xen support is enabled, QEMU changes hypervisor identification (CPUID 0x40000000..0x4000000A) to Xen. The KVM identification and features are not @@ -33,11 +35,25 @@ moves to leaves 0x40000100..0x4000010A. The Xen platform device is enabled automatically for a Xen guest. This allows a guest to unplug all emulated devices, in order to use Xen PV block and network -drivers instead. Note that until the Xen PV device back ends are enabled to work -with Xen mode in QEMU, that is unlikely to cause significant joy. Linux guests -can be dissuaded from this by adding 'xen_emul_unplug=never' on their command -line, and it can also be noted that AHCI disk controllers are exempt from being -unplugged, as are passthrough VFIO PCI devices. +drivers instead. Under Xen, the boot disk is typically available both via IDE +emulation, and as a PV block device. Guest bootloaders typically use IDE to load +the guest kernel, which then unplugs the IDE and continues with the Xen PV block +device. + +This configuration can be achieved as follows + +.. parsed-literal:: + + |qemu_system| -M pc --accel kvm,xen-version=0x4000a,kernel-irqchip=split \\ + -drive file=${GUEST_IMAGE},if=none,id=disk,file.locking=off -device xen-disk,drive=disk,vdev=xvda \\ + -drive file=${GUEST_IMAGE},index=2,media=disk,file.locking=off,if=ide + +It is necessary to use the pc machine type, as the q35 machine uses AHCI instead +of legacy IDE, and AHCI disks are not unplugged through the Xen PV unplug +mechanism. + +VirtIO devices can also be used; Linux guests may need to be dissuaded from +umplugging them by adding 'xen_emul_unplug=never' on their command line. Properties ---------- diff --git a/docs/system/target-mips.rst b/docs/system/target-mips.rst index 138441bdec..83239fb9df 100644 --- a/docs/system/target-mips.rst +++ b/docs/system/target-mips.rst @@ -8,8 +8,6 @@ endian options, ``qemu-system-mips``, ``qemu-system-mipsel`` ``qemu-system-mips64`` and ``qemu-system-mips64el``. Five different machine types are emulated: -- A generic ISA PC-like machine \"mips\" - - The MIPS Malta prototype board \"malta\" - An ACER Pica \"pica61\". This machine needs the 64-bit emulator. @@ -19,18 +17,6 @@ machine types are emulated: - A MIPS Magnum R4000 machine \"magnum\". This machine needs the 64-bit emulator. -The generic emulation is supported by Debian 'Etch' and is able to -install Debian into a virtual disk image. The following devices are -emulated: - -- A range of MIPS CPUs, default is the 24Kf - -- PC style serial port - -- PC style IDE disk - -- NE2000 network card - The Malta emulation supports the following devices: - Core board with MIPS 24Kf CPU and Galileo system controller |