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Subject: Re: [PATCH RFC 0/4] KVM: MIPS: Provide arch-specific
 kvm_flush_remote_tlbs()
To:     Paolo Bonzini <pbonzini@redhat.com>,
        Paul Burton <paulburton@kernel.org>,
        Mike Rapoport <rppt@linux.ibm.com>
Cc:     Peter Xu <peterx@redhat.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        linux-mips@vger.kernel.org, Vitaly Kuznetsov <vkuznets@redhat.com>
References: <20200207223520.735523-1-peterx@redhat.com>
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Date:   Wed, 12 Feb 2020 20:02:34 +0100
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On 2/12/20 5:40 PM, Paolo Bonzini wrote:
> On 12/02/20 17:30, Paul Burton wrote:
>> Hi Paolo,
>>
>> On Wed, Feb 12, 2020 at 01:25:30PM +0100, Paolo Bonzini wrote:
>>> MIPS folks, I see that arch/mips/kvm/mmu.c uses pud_index, so it's not
>>> clear to me if it's meant to only work if CONFIG_PGTABLE_LEVELS=4 or
>>> it's just bit rot.  Should I add a "depends on PGTABLE_LEVEL=4" to
>>> arch/mips/Kconfig?
>>
>> I'm no expert on this bit of code, but I'm pretty sure the systems
>> KVM/VZ has been used on the most internally had PGTABLE_LEVEL=3.
>>
>> I suspect this is actually a regression from commit 31168f033e37 ("mips:
>> drop __pXd_offset() macros that duplicate pXd_index() ones"). Whilst
>> that commit is correct that pud_index() & __pud_offset() are the same
>> when pud_index() is actually provided, it doesn't take into account the
>> __PAGETABLE_PUD_FOLDED case. There __pud_offset() was available but
>> would always evaluate to zero, whereas pud_index() isn't defined...
> 
> Ok, I'll try to whip out a patch that handles __PAGETABLE_PUD_FOLDED.
> On the other hand this makes me worry about how much KVM is being tested
> by people that care about MIPS (even just compile-tested).

FYI last time James confirmed he tested QEMU was in 2017:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg477133.html

At the end of 2019 he orphaned the QEMU part:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg667240.html
and dropped the kernel maintainance:
https://git.kernel.org/pub/scm/linux/kernel/git/mips/linux.git/commit/?id=9c48c48cd499