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Re: [PATCH 00/20] KVM for MIPS32 Processors

To: Sanjay Lal <>
Subject: Re: [PATCH 00/20] KVM for MIPS32 Processors
From: Avi Kivity <>
Date: Thu, 01 Nov 2012 16:51:47 +0200
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On 10/31/2012 05:17 PM, Sanjay Lal wrote:
> The following patchset implements KVM support for MIPS32R2 processors,
> using Trap & Emulate, with basic runtime binary translation to improve
> performance.  The goal has been to keep the Guest kernel changes to a
> minimum.
> The patch is against Linux 3.7-rc2.  
> There is a companion patchset for QEMU that adds KVM support for the 
> MIPS target.
> KVM/MIPS should support MIPS32-R2 processors and beyond.
> It has been tested on the following platforms:
>   - Malta Board with FPGA based 34K (Little Endian).
>   - Sigma Designs TangoX board with a 24K based 8654 SoC (Little Endian).
>   - Malta Board with 74K @ 1GHz (Little Endian).
>   - OVPSim MIPS simulator from Imperas emulating a Malta board with 
>     24Kc and 1074Kc cores (Little Endian).
> Both Guest kernel and Guest Userspace execute in UM. The Guest address space 
> is
> as folows:
>  Guest User address space:   0x00000000 -> 0x40000000
>  Guest Kernel Unmapped:      0x40000000 -> 0x60000000
>  Guest Kernel Mapped:        0x60000000 -> 0x80000000
> As a result, Guest Usermode virtual memory is limited to 1GB.
> Relase Notes
> ============
> (1) 16K Page Size:
>     Both Host Kernel and Guest Kernel should have the same page size, 
>     currently at least 16K.  Note that due to cache aliasing issues, 
>     4K page sizes are NOT supported.
> (2) No HugeTLB/Large Page Support:
>     Both the host kernel and Guest kernel should have the page size 
>     set to at least 16K.
>     This will be implemented in a future release.
> (3) SMP Guests to not work
>     Linux-3.7-rc2 based SMP guest hangs due to the following code sequence 
>     in the generated TLB handlers:
>          LL/TLBP/SC
>     Since the TLBP instruction causes a trap the reservation gets cleared
>     when we ERET back to the guest. This causes the guest to hang in an 
>     infinite loop.
>     As a workaround, make sure that CONFIG_SMP is disabled for Guest kernels.
>     This will be fixed in a future release.
> (4) FPU support:
>     Currently KVM/MIPS emulates a 24K CPU without a FPU.
>     This will be fixed in a future release

Thanks for posting this, new architectures are always a welcome addition.

Some general notes:
- please read and follow Documentation/CodingStyle.  In general the
patches are okay except for indentation (use tabs, not spaces, and set
your editor tab width to 8).
- please use 'git send-email' to send the entire patchset, this keeps
all the patches in a single thread which is easier to follow.
- please add a general architecture document to Documentation/virtual/kvm
- Update Documentation/virtual/kvm/api.txt as needed.

What is the intended use case?

error compiling committee.c: too many arguments to function

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