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

To: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH 00/20] KVM for MIPS32 Processors
From: Sanjay Lal <sanjayl@kymasys.com>
Date: Fri, 2 Nov 2012 13:14:09 -0400
Cc: kvm@vger.kernel.org, linux-mips@linux-mips.org
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On Nov 1, 2012, at 10:51 AM, Avi Kivity wrote:

> 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).

I'll definitely be re-formatting the code based on the recommended coding style 
and running the patches through checkpatch.pl for v2 of the patch set.

Regards
Sanjay


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