From: Marcelo Tosatti <mtosatti@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>,
LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org>
Subject: Re: [PATCH v5 00/12] KVM: introduce readonly memslot
Date: Thu, 16 Aug 2012 12:57:40 -0300 [thread overview]
Message-ID: <20120816155739.GA23247@amt.cnet> (raw)
In-Reply-To: <502CB745.8060709@redhat.com>
On Thu, Aug 16, 2012 at 12:03:01PM +0300, Avi Kivity wrote:
> On 08/15/2012 08:53 PM, Marcelo Tosatti wrote:
> > On Wed, Aug 15, 2012 at 01:44:14PM +0300, Avi Kivity wrote:
> >> On 08/14/2012 06:51 PM, Marcelo Tosatti wrote:
> >> >>
> >> >> 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.
> >> >
> >> > Right, can do that with multiple userspace maps to the same anonymous
> >> > memory region (see other email).
> >>
> >> Yes it's possible. It requires that we move all memory allocation to be
> >> fd based, since userspace can't predict what memory will be dual-mapped
> >> (at least if emulated hardware allows this).
> >
> > It can:
> > - Create named memory object, with associated fd.
> > - Copy data from large anonymous memory region to named memory.
>
> That doesn't work if dma is in progress (assigned device). It also
> doubles the amount of memory in use.
>
> > - Unmap region that must be dual-mapped from large anonymous memory chunk.
> > - Map named memory object at address.
> >
> > The last step can be replaced by adjusting KVM memory slots.
> >
> > The disadvantage of protection information in memory slots
> > is that it duplicates functionality that is handled by
> > userspace mappings.
>
> Agree. So does the memory slots mechanism, and even dirty logging.
>
> > Moreover, multiple memory maps are necessary for any
> > split-qemu-into-smaller-pieces solutions.
>
> Complex users can use complex mechanism, but let's keep the simple stuff
> simple.
>
> >
> >> Is this a reasonable
> >> requirement? Do ksm/thp/autonuma work with this?
> >
> > As mentioned, only memory used for ROM purposes must be dual mapped.
> >
> > I don't think there is any way to create multiple mappings
> > to one anonymous memory object ATM, but POSIX defines it
> > (posix_typed_mem_open).
> >
> > The limitation of thp/ksm on shared memory also affects any other user
> > of shared memory, so it should be fixed there.
> >
> > Also, QEMU ROM is allocated separately from RAM, correct?
> >
>
> Correct. But the chipset is also able to to write-protect some ranges
> in the 0xc0000-0x100000 area via the PAM. It is able to write-protect
> both RAM and PCI memory (usually mapped to flash).
You are convinced that adding read-write protection information to the
memory slots, which controls access by the guest, in addition to the
userspace host pagetables, is useful. OK.
next prev parent reply other threads:[~2012-08-16 16:00 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-07 9:47 [PATCH v5 00/12] KVM: introduce readonly memslot Xiao Guangrong
2012-08-07 9:48 ` [PATCH v5 01/12] KVM: fix missing check for memslot flags Xiao Guangrong
2012-08-07 9:48 ` [PATCH v5 02/12] KVM: hide KVM_MEMSLOT_INVALID from userspace Xiao Guangrong
2012-08-09 18:48 ` Marcelo Tosatti
2012-08-10 2:11 ` Xiao Guangrong
2012-08-07 9:49 ` [PATCH v5 03/12] KVM: introduce gfn_to_pfn_memslot_atomic Xiao Guangrong
2012-08-09 18:50 ` Marcelo Tosatti
2012-08-10 3:22 ` Xiao Guangrong
2012-08-07 9:50 ` [PATCH v5 04/12] KVM: introduce gfn_to_hva_read/kvm_read_hva/kvm_read_hva_atomic Xiao Guangrong
2012-08-07 9:51 ` [PATCH v5 05/12] KVM: reorganize hva_to_pfn Xiao Guangrong
2012-08-10 17:51 ` Marcelo Tosatti
2012-08-11 3:11 ` Xiao Guangrong
2012-08-07 9:51 ` [PATCH v5 06/12] KVM: use 'writable' as a hint to map writable pfn Xiao Guangrong
2012-08-07 9:52 ` [PATCH v5 07/12] KVM: introduce KVM_PFN_ERR_RO_FAULT Xiao Guangrong
2012-08-07 9:52 ` [PATCH v5 08/12] KVM: introduce KVM_HVA_ERR_BAD Xiao Guangrong
2012-08-07 9:53 ` [PATCH v5 09/12] KVM: introduce KVM_HVA_ERR_RO_BAD Xiao Guangrong
2012-08-07 9:54 ` [PATCH v5 10/12] KVM: introduce readonly memslot Xiao Guangrong
2012-08-07 9:54 ` [PATCH v5 11/12] KVM: x86: introduce set_mmio_exit_info Xiao Guangrong
2012-08-10 18:03 ` Marcelo Tosatti
2012-08-11 3:13 ` Xiao Guangrong
2012-08-07 9:55 ` [PATCH v5 12/12] KVM: indicate readonly access fault Xiao Guangrong
2012-08-10 18:14 ` [PATCH v5 00/12] KVM: introduce readonly memslot Marcelo Tosatti
2012-08-11 3:36 ` Xiao Guangrong
2012-08-13 17:39 ` Marcelo Tosatti
2012-08-14 2:58 ` Xiao Guangrong
2012-08-14 15:25 ` Marcelo Tosatti
2012-08-16 5:49 ` Xiao Guangrong
2012-08-16 16:03 ` Marcelo Tosatti
2012-08-14 14:00 ` Avi Kivity
2012-08-14 15:51 ` Marcelo Tosatti
2012-08-15 10:44 ` Avi Kivity
2012-08-15 17:53 ` Marcelo Tosatti
2012-08-16 9:03 ` Avi Kivity
2012-08-16 15:57 ` Marcelo Tosatti [this message]
2012-08-16 16:17 ` Avi Kivity
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