From: "Edgar E. Iglesias" <edgar.iglesias@amd.com>
Reserve memory ranges and interrupt lines for an externally
emulated PCI controller (e.g by QEMU) dedicated to hosting
Virtio devices and potentially other emulated devices.
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
---
xen/include/public/arch-arm.h | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index e19f0251a6..654b827715 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -494,6 +494,20 @@ typedef uint64_t xen_callback_t;
#define GUEST_RAM1_BASE xen_mk_ullong(0x0200000000) /* 952GB of RAM @ 8GB */
#define GUEST_RAM1_SIZE xen_mk_ullong(0xee00000000)
+/* Virtio PCI - Ordered by decreasing size to keep things aligned */
+#define GUEST_VIRTIO_PCI_PREFETCH_MEM_TYPE xen_mk_ullong(0x43000000)
+#define GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE xen_mk_ullong(0x0f000000000)
+#define GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE xen_mk_ullong(0x100000000)
+
+#define GUEST_VIRTIO_PCI_ECAM_BASE (GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE + \
+ GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE)
+#define GUEST_VIRTIO_PCI_ECAM_SIZE xen_mk_ullong(0x10000000)
+
+#define GUEST_VIRTIO_PCI_MEM_TYPE xen_mk_ullong(0x02000000)
+#define GUEST_VIRTIO_PCI_MEM_BASE (GUEST_VIRTIO_PCI_ECAM_BASE + \
+ GUEST_VIRTIO_PCI_ECAM_SIZE)
+#define GUEST_VIRTIO_PCI_MEM_SIZE xen_mk_ullong(0x00002000000)
+
#define GUEST_RAM_BASE GUEST_RAM0_BASE /* Lowest RAM address */
/* Largest amount of actual RAM, not including holes */
#define GUEST_RAM_MAX (GUEST_RAM0_SIZE + GUEST_RAM1_SIZE)
@@ -529,6 +543,9 @@ typedef uint64_t xen_callback_t;
#define GUEST_FFA_NOTIF_PEND_INTR_ID 8
#define GUEST_FFA_SCHEDULE_RECV_INTR_ID 9
+#define GUEST_VIRTIO_PCI_SPI_FIRST 44
+#define GUEST_VIRTIO_PCI_SPI_LAST 48
+
/* PSCI functions */
#define PSCI_cpu_suspend 0
#define PSCI_cpu_off 1
--
2.43.0Hi Edgar, On 24/09/2024 17:23, Edgar E. Iglesias wrote: > From: "Edgar E. Iglesias" <edgar.iglesias@amd.com> > > Reserve memory ranges and interrupt lines for an externally > emulated PCI controller (e.g by QEMU) dedicated to hosting > Virtio devices and potentially other emulated devices. > > Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com> > --- > xen/include/public/arch-arm.h | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h > index e19f0251a6..654b827715 100644 > --- a/xen/include/public/arch-arm.h > +++ b/xen/include/public/arch-arm.h > @@ -494,6 +494,20 @@ typedef uint64_t xen_callback_t; > #define GUEST_RAM1_BASE xen_mk_ullong(0x0200000000) /* 952GB of RAM @ 8GB */ > #define GUEST_RAM1_SIZE xen_mk_ullong(0xee00000000) > > +/* Virtio PCI - Ordered by decreasing size to keep things aligned */ > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_TYPE xen_mk_ullong(0x43000000) > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE xen_mk_ullong(0x0f000000000) > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE xen_mk_ullong(0x100000000) > + > +#define GUEST_VIRTIO_PCI_ECAM_BASE (GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE + \ > + GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE) > +#define GUEST_VIRTIO_PCI_ECAM_SIZE xen_mk_ullong(0x10000000) > + > +#define GUEST_VIRTIO_PCI_MEM_TYPE xen_mk_ullong(0x02000000) > +#define GUEST_VIRTIO_PCI_MEM_BASE (GUEST_VIRTIO_PCI_ECAM_BASE + \ > + GUEST_VIRTIO_PCI_ECAM_SIZE) > +#define GUEST_VIRTIO_PCI_MEM_SIZE xen_mk_ullong(0x00002000000) Why is this specific to virtio PCI? However, I am not entirely convinced we should have a second PCI hostbridge exposed to the guest for a few reasons: 1. This require to reserve yet another range in the address space (could be solved with a more dynamic layout) 2. From your instructions, the guest needs to explicitly do a PCI rescan. So rather than having a second hostbridge, have you considered to extend the existing hostbridge (implemented in Xen) to support a mix of physical PCI device and virtual one? Cheers, -- Julien Grall
On Tue, Sep 24, 2024 at 05:35:20PM +0100, Julien Grall wrote: > Hi Edgar, > > On 24/09/2024 17:23, Edgar E. Iglesias wrote: > > From: "Edgar E. Iglesias" <edgar.iglesias@amd.com> > > > > Reserve memory ranges and interrupt lines for an externally > > emulated PCI controller (e.g by QEMU) dedicated to hosting > > Virtio devices and potentially other emulated devices. > > > > Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com> > > --- > > xen/include/public/arch-arm.h | 17 +++++++++++++++++ > > 1 file changed, 17 insertions(+) > > > > diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h > > index e19f0251a6..654b827715 100644 > > --- a/xen/include/public/arch-arm.h > > +++ b/xen/include/public/arch-arm.h > > @@ -494,6 +494,20 @@ typedef uint64_t xen_callback_t; > > #define GUEST_RAM1_BASE xen_mk_ullong(0x0200000000) /* 952GB of RAM @ 8GB */ > > #define GUEST_RAM1_SIZE xen_mk_ullong(0xee00000000) > > +/* Virtio PCI - Ordered by decreasing size to keep things aligned */ > > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_TYPE xen_mk_ullong(0x43000000) > > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE xen_mk_ullong(0x0f000000000) > > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE xen_mk_ullong(0x100000000) > > + > > +#define GUEST_VIRTIO_PCI_ECAM_BASE (GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE + \ > > + GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE) > > +#define GUEST_VIRTIO_PCI_ECAM_SIZE xen_mk_ullong(0x10000000) > > + > > +#define GUEST_VIRTIO_PCI_MEM_TYPE xen_mk_ullong(0x02000000) > > +#define GUEST_VIRTIO_PCI_MEM_BASE (GUEST_VIRTIO_PCI_ECAM_BASE + \ > > + GUEST_VIRTIO_PCI_ECAM_SIZE) > > +#define GUEST_VIRTIO_PCI_MEM_SIZE xen_mk_ullong(0x00002000000) > > Why is this specific to virtio PCI? However, I am not entirely convinced we > should have a second PCI hostbridge exposed to the guest for a few reasons: > 1. This require to reserve yet another range in the address space (could > be solved with a more dynamic layout) > 2. From your instructions, the guest needs to explicitly do a PCI rescan. > > So rather than having a second hostbridge, have you considered to extend the > existing hostbridge (implemented in Xen) to support a mix of physical PCI > device and virtual one? > Thanks Julien, It's briefly come up in a couple of discussions but I haven't looked carefully at it. It is a good idea and it's probably worth prototyping to see what the gaps are in hypercall interfaces, QEMU support etc. Cheers, Edgar
Hi Edgar, On 24/09/2024 18:11, Edgar E. Iglesias wrote: > On Tue, Sep 24, 2024 at 05:35:20PM +0100, Julien Grall wrote: >> Hi Edgar, >> >> On 24/09/2024 17:23, Edgar E. Iglesias wrote: >>> From: "Edgar E. Iglesias" <edgar.iglesias@amd.com> >>> >>> Reserve memory ranges and interrupt lines for an externally >>> emulated PCI controller (e.g by QEMU) dedicated to hosting >>> Virtio devices and potentially other emulated devices. >>> >>> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com> >>> --- >>> xen/include/public/arch-arm.h | 17 +++++++++++++++++ >>> 1 file changed, 17 insertions(+) >>> >>> diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h >>> index e19f0251a6..654b827715 100644 >>> --- a/xen/include/public/arch-arm.h >>> +++ b/xen/include/public/arch-arm.h >>> @@ -494,6 +494,20 @@ typedef uint64_t xen_callback_t; >>> #define GUEST_RAM1_BASE xen_mk_ullong(0x0200000000) /* 952GB of RAM @ 8GB */ >>> #define GUEST_RAM1_SIZE xen_mk_ullong(0xee00000000) >>> +/* Virtio PCI - Ordered by decreasing size to keep things aligned */ >>> +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_TYPE xen_mk_ullong(0x43000000) >>> +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE xen_mk_ullong(0x0f000000000) >>> +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE xen_mk_ullong(0x100000000) >>> + >>> +#define GUEST_VIRTIO_PCI_ECAM_BASE (GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE + \ >>> + GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE) >>> +#define GUEST_VIRTIO_PCI_ECAM_SIZE xen_mk_ullong(0x10000000) >>> + >>> +#define GUEST_VIRTIO_PCI_MEM_TYPE xen_mk_ullong(0x02000000) >>> +#define GUEST_VIRTIO_PCI_MEM_BASE (GUEST_VIRTIO_PCI_ECAM_BASE + \ >>> + GUEST_VIRTIO_PCI_ECAM_SIZE) >>> +#define GUEST_VIRTIO_PCI_MEM_SIZE xen_mk_ullong(0x00002000000) >> >> Why is this specific to virtio PCI? However, I am not entirely convinced we >> should have a second PCI hostbridge exposed to the guest for a few reasons: >> 1. This require to reserve yet another range in the address space (could >> be solved with a more dynamic layout) >> 2. From your instructions, the guest needs to explicitly do a PCI rescan. Another big advantage I forgot to mention is disaggregation. In a world where the hostbridge is handled in Xen, you could have a PCI device emulated by dom0 while the other is emulated by a stub domain. >> >> So rather than having a second hostbridge, have you considered to extend the >> existing hostbridge (implemented in Xen) to support a mix of physical PCI >> device and virtual one? >> > > Thanks Julien, > > It's briefly come up in a couple of discussions but I haven't looked > carefully at it. It is a good idea and it's probably worth prototyping > to see what the gaps are in hypercall interfaces, QEMU support etc. I also vaguely recall to discuss it on xen-devel. But I couldn't find the discussion... :(. I think all the hypercalls should be there but will require some plumbing in Xen on Arm. QEMU should be able to request Xen to forward configuration access for a given PCI device (see XEN_DMOP_IO_RANGE_PCI). They will then be forwarded to QEMU using IOREQ_TYPE_PCI_CONFIG. We also have an hypercall to be able to inject interrupts from QEMU (see XEN_DMOP_set_irq_level). Cheers, -- Julien Grall
On Tue, 24 Sep 2024, Julien Grall wrote: > On 24/09/2024 18:11, Edgar E. Iglesias wrote: > > On Tue, Sep 24, 2024 at 05:35:20PM +0100, Julien Grall wrote: > > > Hi Edgar, > > > > > > On 24/09/2024 17:23, Edgar E. Iglesias wrote: > > > > From: "Edgar E. Iglesias" <edgar.iglesias@amd.com> > > > > > > > > Reserve memory ranges and interrupt lines for an externally > > > > emulated PCI controller (e.g by QEMU) dedicated to hosting > > > > Virtio devices and potentially other emulated devices. > > > > > > > > Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com> > > > > --- > > > > xen/include/public/arch-arm.h | 17 +++++++++++++++++ > > > > 1 file changed, 17 insertions(+) > > > > > > > > diff --git a/xen/include/public/arch-arm.h > > > > b/xen/include/public/arch-arm.h > > > > index e19f0251a6..654b827715 100644 > > > > --- a/xen/include/public/arch-arm.h > > > > +++ b/xen/include/public/arch-arm.h > > > > @@ -494,6 +494,20 @@ typedef uint64_t xen_callback_t; > > > > #define GUEST_RAM1_BASE xen_mk_ullong(0x0200000000) /* 952GB of RAM > > > > @ 8GB */ > > > > #define GUEST_RAM1_SIZE xen_mk_ullong(0xee00000000) > > > > +/* Virtio PCI - Ordered by decreasing size to keep things aligned */ > > > > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_TYPE xen_mk_ullong(0x43000000) > > > > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE > > > > xen_mk_ullong(0x0f000000000) > > > > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE xen_mk_ullong(0x100000000) > > > > + > > > > +#define GUEST_VIRTIO_PCI_ECAM_BASE > > > > (GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE + \ > > > > + > > > > GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE) > > > > +#define GUEST_VIRTIO_PCI_ECAM_SIZE xen_mk_ullong(0x10000000) > > > > + > > > > +#define GUEST_VIRTIO_PCI_MEM_TYPE xen_mk_ullong(0x02000000) > > > > +#define GUEST_VIRTIO_PCI_MEM_BASE (GUEST_VIRTIO_PCI_ECAM_BASE + > > > > \ > > > > + GUEST_VIRTIO_PCI_ECAM_SIZE) > > > > +#define GUEST_VIRTIO_PCI_MEM_SIZE xen_mk_ullong(0x00002000000) > > > > > > Why is this specific to virtio PCI? However, I am not entirely convinced > > > we > > > should have a second PCI hostbridge exposed to the guest for a few > > > reasons: > > > 1. This require to reserve yet another range in the address space > > > (could > > > be solved with a more dynamic layout) > > > 2. From your instructions, the guest needs to explicitly do a PCI > > > rescan. > > Another big advantage I forgot to mention is disaggregation. In a world where > the hostbridge is handled in Xen, you could have a PCI device emulated by dom0 > while the other is emulated by a stub domain. > > > > > > > So rather than having a second hostbridge, have you considered to extend > > > the > > > existing hostbridge (implemented in Xen) to support a mix of physical PCI > > > device and virtual one? > > > > > > > Thanks Julien, > > > > It's briefly come up in a couple of discussions but I haven't looked > > carefully at it. It is a good idea and it's probably worth prototyping > > to see what the gaps are in hypercall interfaces, QEMU support etc. > > I also vaguely recall to discuss it on xen-devel. But I couldn't find the > discussion... :(. > > I think all the hypercalls should be there but will require some plumbing in > Xen on Arm. QEMU should be able to request Xen to forward configuration access > for a given PCI device (see XEN_DMOP_IO_RANGE_PCI). They will then be > forwarded to QEMU using IOREQ_TYPE_PCI_CONFIG. > > We also have an hypercall to be able to inject interrupts from QEMU (see > XEN_DMOP_set_irq_level). Hi Julien, Yes, I remember a thread on xen-devel too about this topic when EPAM suggested a similar two-hostbridges approach. I was one of the people suggesting to use a single hostbridge at the time. However, when we looked at the implementation more closely, the two-hostbridge approach was easier to get up and running. It works (almost) out of the box. Currently, we have the two-hostbridge solution working on both ARM and x86 to enable virtio-pci to work alongside vPCI in Dom0less/Hyperlaunch configurations. While I think that a single hostbridge is better architecturally, it is important to consider that virtio is moving toward a new transport (virtio-msg, Bertrand is also involved) which does not require a hostbridge. This new transport is key for all our use-cases as it addresses safety requirements and supports AMP configurations without a shared hypervisor between the frontend and backend. Edgar is one of the top contributors to virtio-msg. Given this, I don't think it's worthwhile to invest much effort in virtio-pci, as it will be replaced soon in embedded applications. Cheers, Stefano
Hi Stefano, On 25/09/2024 00:16, Stefano Stabellini wrote: > On Tue, 24 Sep 2024, Julien Grall wrote: >> On 24/09/2024 18:11, Edgar E. Iglesias wrote: >>> On Tue, Sep 24, 2024 at 05:35:20PM +0100, Julien Grall wrote: >>>> Hi Edgar, >>>> >>>> On 24/09/2024 17:23, Edgar E. Iglesias wrote: >>>>> From: "Edgar E. Iglesias" <edgar.iglesias@amd.com> >>>>> >>>>> Reserve memory ranges and interrupt lines for an externally >>>>> emulated PCI controller (e.g by QEMU) dedicated to hosting >>>>> Virtio devices and potentially other emulated devices. >>>>> >>>>> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com> >>>>> --- >>>>> xen/include/public/arch-arm.h | 17 +++++++++++++++++ >>>>> 1 file changed, 17 insertions(+) >>>>> >>>>> diff --git a/xen/include/public/arch-arm.h >>>>> b/xen/include/public/arch-arm.h >>>>> index e19f0251a6..654b827715 100644 >>>>> --- a/xen/include/public/arch-arm.h >>>>> +++ b/xen/include/public/arch-arm.h >>>>> @@ -494,6 +494,20 @@ typedef uint64_t xen_callback_t; >>>>> #define GUEST_RAM1_BASE xen_mk_ullong(0x0200000000) /* 952GB of RAM >>>>> @ 8GB */ >>>>> #define GUEST_RAM1_SIZE xen_mk_ullong(0xee00000000) >>>>> +/* Virtio PCI - Ordered by decreasing size to keep things aligned */ >>>>> +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_TYPE xen_mk_ullong(0x43000000) >>>>> +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE >>>>> xen_mk_ullong(0x0f000000000) >>>>> +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE xen_mk_ullong(0x100000000) >>>>> + >>>>> +#define GUEST_VIRTIO_PCI_ECAM_BASE >>>>> (GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE + \ >>>>> + >>>>> GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE) >>>>> +#define GUEST_VIRTIO_PCI_ECAM_SIZE xen_mk_ullong(0x10000000) >>>>> + >>>>> +#define GUEST_VIRTIO_PCI_MEM_TYPE xen_mk_ullong(0x02000000) >>>>> +#define GUEST_VIRTIO_PCI_MEM_BASE (GUEST_VIRTIO_PCI_ECAM_BASE + >>>>> \ >>>>> + GUEST_VIRTIO_PCI_ECAM_SIZE) >>>>> +#define GUEST_VIRTIO_PCI_MEM_SIZE xen_mk_ullong(0x00002000000) >>>> >>>> Why is this specific to virtio PCI? However, I am not entirely convinced >>>> we >>>> should have a second PCI hostbridge exposed to the guest for a few >>>> reasons: >>>> 1. This require to reserve yet another range in the address space >>>> (could >>>> be solved with a more dynamic layout) >>>> 2. From your instructions, the guest needs to explicitly do a PCI >>>> rescan. >> >> Another big advantage I forgot to mention is disaggregation. In a world where >> the hostbridge is handled in Xen, you could have a PCI device emulated by dom0 >> while the other is emulated by a stub domain. >> >>>> >>>> So rather than having a second hostbridge, have you considered to extend >>>> the >>>> existing hostbridge (implemented in Xen) to support a mix of physical PCI >>>> device and virtual one? >>>> >>> >>> Thanks Julien, >>> >>> It's briefly come up in a couple of discussions but I haven't looked >>> carefully at it. It is a good idea and it's probably worth prototyping >>> to see what the gaps are in hypercall interfaces, QEMU support etc. >> >> I also vaguely recall to discuss it on xen-devel. But I couldn't find the >> discussion... :(. >> >> I think all the hypercalls should be there but will require some plumbing in >> Xen on Arm. QEMU should be able to request Xen to forward configuration access >> for a given PCI device (see XEN_DMOP_IO_RANGE_PCI). They will then be >> forwarded to QEMU using IOREQ_TYPE_PCI_CONFIG. >> >> We also have an hypercall to be able to inject interrupts from QEMU (see >> XEN_DMOP_set_irq_level). > > Hi Julien, > > Yes, I remember a thread on xen-devel too about this topic when EPAM > suggested a similar two-hostbridges approach. I was one of the people > suggesting to use a single hostbridge at the time. > > However, when we looked at the implementation more closely, the > two-hostbridge approach was easier to get up and running. It works > (almost) out of the box. Currently, we have the two-hostbridge solution > working on both ARM and x86 to enable virtio-pci to work alongside vPCI > in Dom0less/Hyperlaunch configurations. I understand this is the easiest solution... However, this requires code in Xen that I am not yet convinced it is good to have. I am not too concerned about the MMIO range part. This can be (easily) solved. I am more concerned about the support of background region and the fact the OS needs to be able to rescan. I am definitely not an expert of PCI, but AFAIK, it is possible to have the guest to be notified when a PCI device is hotplug. Why can't we use it? > > While I think that a single hostbridge is better architecturally, it is > important to consider that virtio is moving toward a new transport > (virtio-msg, Bertrand is also involved) which does not require a > hostbridge. This new transport is key for all our use-cases as it > addresses safety requirements and supports AMP configurations without a > shared hypervisor between the frontend and backend. Edgar is one of the > top contributors to virtio-msg. Given this, I don't think it's > worthwhile to invest much effort in virtio-pci, as it will be replaced > soon in embedded applications. To me this raises the question why we should have a temporary solution upstream then? Cheers, -- Julien Grall
On Wed, 25 Sep 2024, Julien Grall wrote: > On 25/09/2024 00:16, Stefano Stabellini wrote: > > On Tue, 24 Sep 2024, Julien Grall wrote: > > > On 24/09/2024 18:11, Edgar E. Iglesias wrote: > > > > On Tue, Sep 24, 2024 at 05:35:20PM +0100, Julien Grall wrote: > > > > > Hi Edgar, > > > > > > > > > > On 24/09/2024 17:23, Edgar E. Iglesias wrote: > > > > > > From: "Edgar E. Iglesias" <edgar.iglesias@amd.com> > > > > > > > > > > > > Reserve memory ranges and interrupt lines for an externally > > > > > > emulated PCI controller (e.g by QEMU) dedicated to hosting > > > > > > Virtio devices and potentially other emulated devices. > > > > > > > > > > > > Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com> > > > > > > --- > > > > > > xen/include/public/arch-arm.h | 17 +++++++++++++++++ > > > > > > 1 file changed, 17 insertions(+) > > > > > > > > > > > > diff --git a/xen/include/public/arch-arm.h > > > > > > b/xen/include/public/arch-arm.h > > > > > > index e19f0251a6..654b827715 100644 > > > > > > --- a/xen/include/public/arch-arm.h > > > > > > +++ b/xen/include/public/arch-arm.h > > > > > > @@ -494,6 +494,20 @@ typedef uint64_t xen_callback_t; > > > > > > #define GUEST_RAM1_BASE xen_mk_ullong(0x0200000000) /* 952GB > > > > > > of RAM > > > > > > @ 8GB */ > > > > > > #define GUEST_RAM1_SIZE xen_mk_ullong(0xee00000000) > > > > > > +/* Virtio PCI - Ordered by decreasing size to keep things aligned > > > > > > */ > > > > > > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_TYPE > > > > > > xen_mk_ullong(0x43000000) > > > > > > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE > > > > > > xen_mk_ullong(0x0f000000000) > > > > > > +#define GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE > > > > > > xen_mk_ullong(0x100000000) > > > > > > + > > > > > > +#define GUEST_VIRTIO_PCI_ECAM_BASE > > > > > > (GUEST_VIRTIO_PCI_PREFETCH_MEM_BASE + \ > > > > > > + > > > > > > GUEST_VIRTIO_PCI_PREFETCH_MEM_SIZE) > > > > > > +#define GUEST_VIRTIO_PCI_ECAM_SIZE xen_mk_ullong(0x10000000) > > > > > > + > > > > > > +#define GUEST_VIRTIO_PCI_MEM_TYPE xen_mk_ullong(0x02000000) > > > > > > +#define GUEST_VIRTIO_PCI_MEM_BASE > > > > > > (GUEST_VIRTIO_PCI_ECAM_BASE + > > > > > > \ > > > > > > + > > > > > > GUEST_VIRTIO_PCI_ECAM_SIZE) > > > > > > +#define GUEST_VIRTIO_PCI_MEM_SIZE > > > > > > xen_mk_ullong(0x00002000000) > > > > > > > > > > Why is this specific to virtio PCI? However, I am not entirely > > > > > convinced > > > > > we > > > > > should have a second PCI hostbridge exposed to the guest for a few > > > > > reasons: > > > > > 1. This require to reserve yet another range in the address space > > > > > (could > > > > > be solved with a more dynamic layout) > > > > > 2. From your instructions, the guest needs to explicitly do a PCI > > > > > rescan. > > > > > > Another big advantage I forgot to mention is disaggregation. In a world > > > where > > > the hostbridge is handled in Xen, you could have a PCI device emulated by > > > dom0 > > > while the other is emulated by a stub domain. > > > > > > > > > > > > > So rather than having a second hostbridge, have you considered to > > > > > extend > > > > > the > > > > > existing hostbridge (implemented in Xen) to support a mix of physical > > > > > PCI > > > > > device and virtual one? > > > > > > > > > > > > > Thanks Julien, > > > > > > > > It's briefly come up in a couple of discussions but I haven't looked > > > > carefully at it. It is a good idea and it's probably worth prototyping > > > > to see what the gaps are in hypercall interfaces, QEMU support etc. > > > > > > I also vaguely recall to discuss it on xen-devel. But I couldn't find the > > > discussion... :(. > > > > > > I think all the hypercalls should be there but will require some plumbing > > > in > > > Xen on Arm. QEMU should be able to request Xen to forward configuration > > > access > > > for a given PCI device (see XEN_DMOP_IO_RANGE_PCI). They will then be > > > forwarded to QEMU using IOREQ_TYPE_PCI_CONFIG. > > > > > > We also have an hypercall to be able to inject interrupts from QEMU (see > > > XEN_DMOP_set_irq_level). > > > > Hi Julien, > > > > Yes, I remember a thread on xen-devel too about this topic when EPAM > > suggested a similar two-hostbridges approach. I was one of the people > > suggesting to use a single hostbridge at the time. > > > > However, when we looked at the implementation more closely, the > > two-hostbridge approach was easier to get up and running. It works > > (almost) out of the box. Currently, we have the two-hostbridge solution > > working on both ARM and x86 to enable virtio-pci to work alongside vPCI > > in Dom0less/Hyperlaunch configurations. > > I understand this is the easiest solution... However, this requires code in > Xen that I am not yet convinced it is good to have. > > I am not too concerned about the MMIO range part. This can be (easily) solved. > I am more concerned about the support of background region and the fact the OS > needs to be able to rescan. > > I am definitely not an expert of PCI, but AFAIK, it is possible to have the > guest to be notified when a PCI device is hotplug. Why can't we use it? Yes, that is the cleanest solution and Xenia has been working on that in the last couple of weeks. I am not sure if she has it fully functional yet. PCI rescan is just a crude but effective way to solve the problem. We also have a prototype of a special "flag" on the PCI root complex to tell the guest if the bus is ready, or whether it should wait. In any case I am confident this issue can be solved well, and we were already aiming for pci hotplug as the final solution. > > While I think that a single hostbridge is better architecturally, it is > > important to consider that virtio is moving toward a new transport > > (virtio-msg, Bertrand is also involved) which does not require a > > hostbridge. This new transport is key for all our use-cases as it > > addresses safety requirements and supports AMP configurations without a > > shared hypervisor between the frontend and backend. Edgar is one of the > > top contributors to virtio-msg. Given this, I don't think it's > > worthwhile to invest much effort in virtio-pci, as it will be replaced > > soon in embedded applications. > > To me this raises the question why we should have a temporary solution > upstream then? Having virtio-pci support as a stopgap seems beneficial, especially since it's reasonable to expect it will be needed for 1-2 years, which is a considerable period. This would put Xen in a good position in respect to other hypervisors in the same space. However, I also recognize that this implementation isn't ideal.
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