[RFC PATCH 0/2] Handle physical address bits

Hello everyone, These patches let one specify how wide the physical addresses are, in bits. Using current QEMU's default of 40 may limit the amount of RAM the guest can see (which is the reason why, in our packages, we bump that to 42; and as far as I've understood from reading some old mailing list threads on the subject, other downstreams do something similar). It also can cause other problems, such as the one described in: https://bugzilla.redhat.com/show_bug.cgi?id=1578278#c5 Basically, the VM thinking and reporting to the user that L1TF is unmitigated, because while its RAM may fits in MAX_PHYS_ADDR (e.g., equal to 42 or 40) it does not fit in MAX_PHYS_ADDR/2, which is necessary for PTE inversion to be effective. I've also mentioned this during my KVM Forum talk (slides 81, 82, from here: http://xenbits.xen.org/people/dariof/talks/Virtual%20Topology%20Friend%20...) The series alleviates the problem by providing an user with an easy way to either specify an arbitrary number of physical address bits bits for the VM (with, e.g., <maxphysaddr mode='emulate' bits='42'/>) or just using the same number of bits of the host (with <maxphysaddr mode='passthrough'/>). This in theory is already possible, but only in an hack-ish way, such as adding: <qemu:commandline> <qemu:arg value='-cpu'/> <qemu:arg value='host,host-phys-bits=on'/> </qemu:commandline> But this is super inconvenient. :-) I have not done it such as host-phys-bits=on is automatically added when using cpu-passthrough as CPU model, as I think that that actually belongs in QEMU. Basically, this works and can be used very much like the <cache/> element. Ah, so, the series is RFC basically because the QEMU capability test is failing. I think I may be failing at understanding how things should work. Or maybe I "just" need to regenerate the files against which capabilities themselves are checked (and if this is the case, I need to understand how). Well, I'll keep looking into this, and try to figure it out (but, if anyone has any hint, that's much appreciated :-P). Feedback welcome. Thanks and Regards --- Dario Faggioli (2): Add support for specifying max physical address size. qemu: Add support for max physical address size src/qemu/qemu_capabilities.c | 2 + src/qemu/qemu_capabilities.h | 1 + src/qemu/qemu_command.c | 28 +++++++++++ src/qemu/qemu_domain.c | 46 +++++++++++++++++++ .../cpu-phys-bits-emulate.args | 29 ++++++++++++ .../cpu-phys-bits-emulate.xml | 20 ++++++++ .../cpu-phys-bits-emulate2.args | 30 ++++++++++++ .../cpu-phys-bits-emulate2.xml | 20 ++++++++ .../cpu-phys-bits-emulate3.err | 1 + .../cpu-phys-bits-emulate3.xml | 20 ++++++++ .../cpu-phys-bits-passthrough.args | 29 ++++++++++++ .../cpu-phys-bits-passthrough.xml | 20 ++++++++ .../cpu-phys-bits-passthrough2.err | 1 + .../cpu-phys-bits-passthrough2.xml | 20 ++++++++ .../cpu-phys-bits-passthrough3.err | 1 + .../cpu-phys-bits-passthrough3.xml | 20 ++++++++ tests/qemuxml2argvtest.c | 7 +++ 17 files changed, 295 insertions(+) create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-emulate.args create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-emulate.xml create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-emulate2.args create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-emulate2.xml create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-emulate3.err create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-emulate3.xml create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-passthrough.args create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-passthrough.xml create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-passthrough2.err create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-passthrough2.xml create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-passthrough3.err create mode 100644 tests/qemuxml2argvdata/cpu-phys-bits-passthrough3.xml -- Dario Faggioli, Ph.D http://about.me/dario.faggioli Virtualization Software Engineer SUSE Labs, SUSE https://www.suse.com/ ------------------------------------------------------------------- <<This happens because _I_ choose it to happen!>> (Raistlin Majere)