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[79.183.34.164]) by smtp.gmail.com with ESMTPSA id b42sm3385141qtb.36.2020.01.09.05.28.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Jan 2020 05:29:00 -0800 (PST) Date: Thu, 9 Jan 2020 08:28:55 -0500 From: "Michael S. Tsirkin" To: "Dr. David Alan Gilbert" Subject: Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device Message-ID: <20200109082810-mutt-send-email-mst@kernel.org> References: <20200108135353.75471-1-dgilbert@redhat.com> <20200108135353.75471-3-dgilbert@redhat.com> <20200109064527-mutt-send-email-mst@kernel.org> <20200109120820.GB6795@work-vm> <20200109071454-mutt-send-email-mst@kernel.org> <20200109122237.GD6795@work-vm> <20200109080412-mutt-send-email-mst@kernel.org> <20200109132242.GF6795@work-vm> <20200109082726-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: <20200109082726-mutt-send-email-mst@kernel.org> X-MC-Unique: vfaqvg5KP-WHUuGtTHVJKQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: jasowang@redhat.com, pbonzini@redhat.com, vkuznets@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jan 09, 2020 at 08:28:00AM -0500, Michael S. Tsirkin wrote: > On Thu, Jan 09, 2020 at 01:22:42PM +0000, Dr. David Alan Gilbert wrote: > > * Michael S. Tsirkin (mst@redhat.com) wrote: > > > On Thu, Jan 09, 2020 at 12:22:37PM +0000, Dr. David Alan Gilbert wrot= e: > > > > * Michael S. Tsirkin (mst@redhat.com) wrote: > > > > > On Thu, Jan 09, 2020 at 12:08:20PM +0000, Dr. David Alan Gilbert = wrote: > > > > > > * Michael S. Tsirkin (mst@redhat.com) wrote: > > > > > > > On Wed, Jan 08, 2020 at 01:53:53PM +0000, Dr. David Alan Gilb= ert (git) wrote: > > > > > > > > From: "Dr. David Alan Gilbert" > > > > > > > >=20 > > > > > > > > Mark the synic pages as ram_device so that they won't be vi= sible > > > > > > > > to vhost. > > > > > > > >=20 > > > > > > > > Signed-off-by: Dr. David Alan Gilbert > > > > > > >=20 > > > > > > >=20 > > > > > > > I think I disagree with this one. > > > > > > > * A RAM device represents a mapping to a physical device, su= ch as to a PCI > > > > > > > * MMIO BAR of an vfio-pci assigned device. The memory regio= n may be mapped > > > > > > > * into the VM address space and access to the region will mo= dify memory > > > > > > > * directly. However, the memory region should not be includ= ed in a memory > > > > > > > * dump (device may not be enabled/mapped at the time of the = dump), and > > > > > > > * operations incompatible with manipulating MMIO should be a= voided. Replaces > > > > > > > * skip_dump flag. > > > > > > >=20 > > > > > > > Looks like an abuse of notation. > > > > > >=20 > > > > > > OK, it did feel a bit like that - any suggestions of another wa= y to do > > > > > > it? > > > > > > This clearly isn't normal RAM. > > > > > >=20 > > > > > > Dave > > > > >=20 > > > > > If it's just an optimization for vhost/postcopy/etc, then I think > > > >=20 > > > > Note it's not an optimisation; postcopy fails unless you can aggreg= ate > > > > the members of the hugepage. > > > > And I think vhost-user will fail if you have too many sections - an= d > > > > the 16 sections from synic I think will blow the slots available. > > >=20 > > > Right, so both are internal reasons. > > >=20 > > > > > an API that says how this isn't normal ram would be ok. > > > > > E.g. it's not DMA'd into? Then maybe _nodma? > > > >=20 > > > > Do we want a new memory_region_init for that or just to be able to = add > > > > a flag? > > > >=20 > > > > Dave > > >=20 > > > 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. > >=20 > > (Copying Paolo in) > > So what exactly does this flag mean; to me it's 'no vhost' - but is it > > actually more general? > >=20 > > Dave >=20 > I think it's also handy for VFIO, that should skip it too. BTW if it's "per cpu" then that is another way to put it. Neither vfio nor vhost have a concept of cpu so neither can support accessing per cpu things. >=20 > > > > > > >=20 > > > > > > >=20 > > > > > > > > --- > > > > > > > > hw/hyperv/hyperv.c | 14 ++++++++------ > > > > > > > > 1 file changed, 8 insertions(+), 6 deletions(-) > > > > > > > >=20 > > > > > > > > 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 =3D g_strdup_printf("synic-%u-msg-page", vp_= index); > > > > > > > > eventp_name =3D g_strdup_printf("synic-%u-event-page",= vp_index); > > > > > > > > =20 > > > > > > > > - memory_region_init_ram(&synic->msg_page_mr, obj, msgp_= name, > > > > > > > > - sizeof(*synic->msg_page), &erro= r_abort); > > > > > > > > - memory_region_init_ram(&synic->event_page_mr, obj, eve= ntp_name, > > > > > > > > - sizeof(*synic->event_page), &er= ror_abort); > > > > > > > > - synic->msg_page =3D memory_region_get_ram_ptr(&synic->= msg_page_mr); > > > > > > > > - synic->event_page =3D memory_region_get_ram_ptr(&synic= ->event_page_mr); > > > > > > > > + synic->msg_page =3D qemu_memalign(qemu_real_host_page_= size, > > > > > > > > + sizeof(*synic->msg_pag= e)); > > > > > > > > + synic->event_page =3D qemu_memalign(qemu_real_host_pag= e_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_m= r, obj, eventp_name, > > > > > > > > + sizeof(*synic->event_page), syn= ic->event_page); > > > > > > > > =20 > > > > > > > > g_free(msgp_name); > > > > > > > > g_free(eventp_name); > > > > > > > > --=20 > > > > > > > > 2.24.1 > > > > > > >=20 > > > > > > -- > > > > > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > > > > >=20 > > > > -- > > > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > > >=20 > > -- > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK