linux-kernel - Re: [PATCH v5 00/12] KVM: introduce readonly memslot

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Message-ID: <502A5A01.6040505@redhat.com>
Date:	Tue, 14 Aug 2012 17:00:33 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v5 00/12] KVM: introduce readonly memslot

On 08/10/2012 09:14 PM, Marcelo Tosatti wrote:
> On Tue, Aug 07, 2012 at 05:47:15PM +0800, Xiao Guangrong wrote:
>> Changelog:
>> - introduce KVM_PFN_ERR_RO_FAULT instead of dummy page
>> - introduce KVM_HVA_ERR_BAD and optimize error hva indicators
>> 
>> The test case can be found at:
>> http://lkml.indiana.edu/hypermail/linux/kernel/1207.2/00819/migrate-perf.tar.bz2
>> 
>> In current code, if we map a readonly memory space from host to guest
>> and the page is not currently mapped in the host, we will get a fault-pfn
>> and async is not allowed, then the vm will crash.
>> 
>> As Avi's suggestion, We introduce readonly memory region to map ROM/ROMD
>> to the guest, read access is happy for readonly memslot, write access on
>> readonly memslot will cause KVM_EXIT_MMIO exit.
> 
> Memory slots whose QEMU mapping is write protected is supported
> today, as long as there are no write faults.
> 
> What prevents the use of mmap(!MAP_WRITE) to handle read-only memslots
> again?

Userspace may want to modify the ROM (for example, when programming a
flash device).  It is also possible to map an hva range rw through one
slot and ro through another.


-- 
error compiling committee.c: too many arguments to function
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