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Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device |
Date: |
Thu, 9 Jan 2020 08:06:25 -0500 |
On Thu, Jan 09, 2020 at 12:22:37PM +0000, Dr. David Alan Gilbert wrote:
> * Michael S. Tsirkin (address@hidden) wrote:
> > On Thu, Jan 09, 2020 at 12:08:20PM +0000, Dr. David Alan Gilbert wrote:
> > > * Michael S. Tsirkin (address@hidden) wrote:
> > > > On Wed, Jan 08, 2020 at 01:53:53PM +0000, Dr. David Alan Gilbert (git)
> > > > wrote:
> > > > > From: "Dr. David Alan Gilbert" <address@hidden>
> > > > >
> > > > > Mark the synic pages as ram_device so that they won't be visible
> > > > > to vhost.
> > > > >
> > > > > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> > > >
> > > >
> > > > I think I disagree with this one.
> > > > * A RAM device represents a mapping to a physical device, such as to a
> > > > PCI
> > > > * MMIO BAR of an vfio-pci assigned device. The memory region may be
> > > > mapped
> > > > * into the VM address space and access to the region will modify memory
> > > > * directly. However, the memory region should not be included in a
> > > > memory
> > > > * dump (device may not be enabled/mapped at the time of the dump), and
> > > > * operations incompatible with manipulating MMIO should be avoided.
> > > > Replaces
> > > > * skip_dump flag.
> > > >
> > > > Looks like an abuse of notation.
> > >
> > > OK, it did feel a bit like that - any suggestions of another way to do
> > > it?
> > > This clearly isn't normal RAM.
> > >
> > > Dave
> >
> > If it's just an optimization for vhost/postcopy/etc, then I think
>
> Note it's not an optimisation; postcopy fails unless you can aggregate
> the members of the hugepage.
> And I think vhost-user will fail if you have too many sections - and
> the 16 sections from synic I think will blow the slots available.
Right, so both are internal reasons.
> > an API that says how this isn't normal ram would be ok.
> > E.g. it's not DMA'd into? Then maybe _nodma?
>
> Do we want a new memory_region_init for that or just to be able to add
> a flag?
>
> Dave
I think a flag API is preferable since this can apply to any kind of
region. But can go either way, Paolo's the maintainer there.
> > > >
> > > >
> > > > > ---
> > > > > hw/hyperv/hyperv.c | 14 ++++++++------
> > > > > 1 file changed, 8 insertions(+), 6 deletions(-)
> > > > >
> > > > > diff --git a/hw/hyperv/hyperv.c b/hw/hyperv/hyperv.c
> > > > > index da8ce82725..4de3ec411d 100644
> > > > > --- a/hw/hyperv/hyperv.c
> > > > > +++ b/hw/hyperv/hyperv.c
> > > > > @@ -95,12 +95,14 @@ static void synic_realize(DeviceState *dev, Error
> > > > > **errp)
> > > > > msgp_name = g_strdup_printf("synic-%u-msg-page", vp_index);
> > > > > eventp_name = g_strdup_printf("synic-%u-event-page", vp_index);
> > > > >
> > > > > - memory_region_init_ram(&synic->msg_page_mr, obj, msgp_name,
> > > > > - sizeof(*synic->msg_page), &error_abort);
> > > > > - memory_region_init_ram(&synic->event_page_mr, obj, eventp_name,
> > > > > - sizeof(*synic->event_page), &error_abort);
> > > > > - synic->msg_page = memory_region_get_ram_ptr(&synic->msg_page_mr);
> > > > > - synic->event_page =
> > > > > memory_region_get_ram_ptr(&synic->event_page_mr);
> > > > > + synic->msg_page = qemu_memalign(qemu_real_host_page_size,
> > > > > + sizeof(*synic->msg_page));
> > > > > + synic->event_page = qemu_memalign(qemu_real_host_page_size,
> > > > > + sizeof(*synic->event_page));
> > > > > + memory_region_init_ram_device_ptr(&synic->msg_page_mr, obj,
> > > > > msgp_name,
> > > > > + sizeof(*synic->msg_page),
> > > > > synic->msg_page);
> > > > > + memory_region_init_ram_device_ptr(&synic->event_page_mr, obj,
> > > > > eventp_name,
> > > > > + sizeof(*synic->event_page),
> > > > > synic->event_page);
> > > > >
> > > > > g_free(msgp_name);
> > > > > g_free(eventp_name);
> > > > > --
> > > > > 2.24.1
> > > >
> > > --
> > > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> >
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, (continued)
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Michael S. Tsirkin, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Dr. David Alan Gilbert, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Michael S. Tsirkin, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Dr. David Alan Gilbert, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Vitaly Kuznetsov, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Roman Kagan, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Dr. David Alan Gilbert, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Roman Kagan, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Dr. David Alan Gilbert, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Roman Kagan, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device,
Michael S. Tsirkin <=
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Dr. David Alan Gilbert, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Michael S. Tsirkin, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Michael S. Tsirkin, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Dr. David Alan Gilbert, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Paolo Bonzini, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Dr. David Alan Gilbert, 2020/01/09
- Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Vitaly Kuznetsov, 2020/01/09
Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device, Roman Kagan, 2020/01/09
Re: [PATCH 0/2] exclude hyperv synic sections from vhost, Vitaly Kuznetsov, 2020/01/08