Re: [Qemu-devel] [PATCH] nvme: 64kB page size fixes

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Tue, Dec 02, 2014 at 09:18:59PM +0100, Paolo Bonzini wrote:
> 
> 
> On 27/11/2014 04:39, Anton Blanchard wrote:
> > Initialise our maximum page size capability to 64kB and increase
> > the page_size variable from 16 to 32 bits.
> > 
> > Signed-off-by: Anton Blanchard <anton@samba.org>
> > --
> > 
> > diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> > index 1327658..aa1ed98 100644
> > --- a/hw/block/nvme.c
> > +++ b/hw/block/nvme.c
> > @@ -811,6 +811,7 @@ static int nvme_init(PCIDevice *pci_dev)
> >      NVME_CAP_SET_AMS(n->bar.cap, 1);
> >      NVME_CAP_SET_TO(n->bar.cap, 0xf);
> >      NVME_CAP_SET_CSS(n->bar.cap, 1);
> > +    NVME_CAP_SET_MPSMAX(n->bar.cap, 4);
> >  
> >      n->bar.vs = 0x00010001;
> >      n->bar.intmc = n->bar.intms = 0;
> > diff --git a/hw/block/nvme.h b/hw/block/nvme.h
> > index 993c511..b6ccb65 100644
> > --- a/hw/block/nvme.h
> > +++ b/hw/block/nvme.h
> > @@ -688,7 +688,7 @@ typedef struct NvmeCtrl {
> >      NvmeBar      bar;
> >      BlockConf    conf;
> >  
> > -    uint16_t    page_size;
> > +    uint32_t    page_size;
> >      uint16_t    page_bits;
> >      uint16_t    max_prp_ents;
> >      uint16_t    cqe_size;
> > 
> > 
> 
> This should probably be a property of the device instead.  If you want
> to change the default, you need to preserve a backwards-compatible value
> for pre-2.3 machine types (-M pc-i440fx-2.2, -M pc-i440fx-2.1 etc.).

Hi Anton,
Any update on this?

Paolo has a point that changing this value would make a guest-visible
hardware change.  Therefore older machine types, which users might rely
on, should continue to show the old value.

This is especially important with live migration because hardware should
not change underneath the guest due to migration.

Stefan

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