Re: [PATCH 00/31] KVM/MIPS: Implement hardware virtualization viathe MIPS-VZ extensions.

From: David Daney
Date: Sun Jun 09 2013 - 19:23:59 EST

On 06/09/2013 12:31 AM, Gleb Natapov wrote:
On Fri, Jun 07, 2013 at 04:15:00PM -0700, David Daney wrote:
I should also add that I will shortly send patches for the kvm tool
required to drive this VM as well as a small set of patches that
create a para-virtualized MIPS/Linux guest kernel.

The idea is that because there is no standard SMP linux system, we
create a standard para-virtualized system that uses a handful of
hypercalls, but mostly just uses virtio devices. It has no emulated
real hardware (no 8250 UART, no emulated legacy anything...)

Virtualization is useful for running legacy code. Why dismiss support
for non pv guests so easily?

Just because we create standard PV system devices, doesn't preclude emulating real hardware. In fact Sanjay Lal's work includes QEMU support for doing just this for a MIPS malta board. I just wanted a very simple system I could implement with the kvm tool in a couple of days, so that is what I initially did.

The problem is that almost nobody has real malta boards, they are really only of interest because QEMU implements a virtual malta board.

Personally, I see the most interesting us cases of MIPS KVM being a deployment platform for new services, so legacy support is not so important to me. That doesn't mean that other people wouldn't want some sort of legacy support. The problem with 'legacy' on MIPS is that there are hundreds of legacies to choose from (Old SGI and DEC hardware, various network hardware from many different vendors, etc.). Which would you choose?

How different MIPS SMP systems are?

o Old SGI heavy metal (several different system architectures).

o Cavium OCTEON SMP SoCs.

o Broadcom (several flavors) SoCs

o Loongson

Come to think of it, Emulating SGI hardware might be an interesting case. There may be old IRIX systems and applications that could be running low on real hardware. Some of those systems take up a whole room and draw a lot of power. They might run faster and at much lower power consumption on a modern 48-Way SMP SoC based system.

about running non pv UP systems?

See above. I think this is what Sanjay Lal is doing.

David Daney

On 06/07/2013 04:03 PM, David Daney wrote:
From: David Daney <david.daney@xxxxxxxxxx>

These patches take a somewhat different approach to MIPS
virtualization via the MIPS-VZ extensions than the patches previously
sent by Sanjay Lal.

Several facts about the code:

o Existing exception handlers are modified to hook in to KVM instead
of intercepting all exceptions via the EBase register, and then
chaining to real exception handlers.

o Able to boot 64-bit SMP guests that use the FPU (I have booted 4-way
SMP 64-bit MIPS/Linux).

o Additional overhead on every exception even when *no* vCPU is running.

o Lower interrupt overhead, than the EBase interception method, when
vCPU *is* running.

o This code is somewhat smaller than the existing trap/emulate
implementation (about 2100 lines vs. about 5300 lines)

o Currently probably only usable on the OCTEON III CPU model, as some
MIPS-VZ implementation-defined behaviors were assumed to have the
OCTEON III behavior.

Note: I think Ralf already has the 17/31 (MIPS: Quit exposing Kconfig
symbols in uapi headers.) queued, but I also include it here.

David Daney (31):
MIPS: Move allocate_kscratch to cpu-probe.c and make it public.
MIPS: Save and restore K0/K1 when CONFIG_KVM_MIPSVZ
mips/kvm: Fix 32-bitisms in kvm_locore.S
mips/kvm: Add casts to avoid pointer width mismatch build failures.
mips/kvm: Use generic cache flushing functions.
mips/kvm: Rename kvm_vcpu_arch.pc to kvm_vcpu_arch.epc
mips/kvm: Rename VCPU_registername to KVM_VCPU_ARCH_registername
mips/kvm: Fix code formatting in arch/mips/kvm/kvm_locore.S
mips/kvm: Factor trap-and-emulate support into a pluggable
mips/kvm: Implement ioctls to get and set FPU registers.
MIPS: Rearrange branch.c so it can be used by kvm code.
MIPS: Add instruction format information for WAIT, MTC0, MFC0, et al.
mips/kvm: Add accessors for MIPS VZ registers.
mips/kvm: Add thread_info flag to indicate operation in MIPS VZ Guest
mips/kvm: Exception handling to leave and reenter guest mode.
mips/kvm: Add exception handler for MIPSVZ Guest exceptions.
MIPS: Quit exposing Kconfig symbols in uapi headers.
mips/kvm: Add pt_regs slots for BadInstr and BadInstrP
mips/kvm: Add host definitions for MIPS VZ based host.
mips/kvm: Hook into TLB fault handlers.
mips/kvm: Allow set_except_vector() to be used from MIPSVZ code.
mips/kvm: Split get_new_mmu_context into two parts.
mips/kvm: Hook into CP unusable exception handler.
mips/kvm: Add thread_struct fields used by MIPSVZ hosts.
mips/kvm: Add some asm-offsets constants used by MIPSVZ.
mips/kvm: Split up Kconfig and Makefile definitions in preperation
mips/kvm: Gate the use of kvm_local_flush_tlb_all() by KVM_MIPSTE
mips/kvm: Add MIPSVZ support.
mips/kvm: Enable MIPSVZ in Kconfig/Makefile
mips/kvm: Allow for upto 8 KVM vcpus per vm.

arch/mips/Kconfig | 1 +
arch/mips/include/asm/branch.h | 7 +
arch/mips/include/asm/kvm_host.h | 622 +-----------
arch/mips/include/asm/kvm_mips_te.h | 589 +++++++++++
arch/mips/include/asm/kvm_mips_vz.h | 29 +
arch/mips/include/asm/mipsregs.h | 264 +++++
arch/mips/include/asm/mmu_context.h | 12 +-
arch/mips/include/asm/processor.h | 6 +
arch/mips/include/asm/ptrace.h | 36 +
arch/mips/include/asm/stackframe.h | 150 ++-
arch/mips/include/asm/thread_info.h | 2 +
arch/mips/include/asm/uasm.h | 2 +-
arch/mips/include/uapi/asm/inst.h | 23 +-
arch/mips/include/uapi/asm/ptrace.h | 17 +-
arch/mips/kernel/asm-offsets.c | 124 ++-
arch/mips/kernel/branch.c | 63 +-
arch/mips/kernel/cpu-probe.c | 34 +
arch/mips/kernel/genex.S | 8 +
arch/mips/kernel/scall64-64.S | 12 +
arch/mips/kernel/scall64-n32.S | 12 +
arch/mips/kernel/traps.c | 15 +-
arch/mips/kvm/Kconfig | 23 +-
arch/mips/kvm/Makefile | 15 +-
arch/mips/kvm/kvm_locore.S | 980 +++++++++---------
arch/mips/kvm/kvm_mips.c | 768 ++------------
arch/mips/kvm/kvm_mips_comm.h | 1 +
arch/mips/kvm/kvm_mips_commpage.c | 9 +-
arch/mips/kvm/kvm_mips_dyntrans.c | 4 +-
arch/mips/kvm/kvm_mips_emul.c | 312 +++---
arch/mips/kvm/kvm_mips_int.c | 53 +-
arch/mips/kvm/kvm_mips_int.h | 2 -
arch/mips/kvm/kvm_mips_stats.c | 6 +-
arch/mips/kvm/kvm_mipsvz.c | 1894 +++++++++++++++++++++++++++++++++++
arch/mips/kvm/kvm_mipsvz_guest.S | 234 +++++
arch/mips/kvm/kvm_tlb.c | 140 +--
arch/mips/kvm/kvm_trap_emul.c | 932 +++++++++++++++--
arch/mips/mm/fault.c | 8 +
arch/mips/mm/tlbex-fault.S | 6 +
arch/mips/mm/tlbex.c | 45 +-
39 files changed, 5299 insertions(+), 2161 deletions(-)
create mode 100644 arch/mips/include/asm/kvm_mips_te.h
create mode 100644 arch/mips/include/asm/kvm_mips_vz.h
create mode 100644 arch/mips/kvm/kvm_mipsvz.c
create mode 100644 arch/mips/kvm/kvm_mipsvz_guest.S

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