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142 lines
5.9 KiB
142 lines
5.9 KiB
From db53345dba5682c3ba0bc3fc596b30a98dadb88f Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= <clg@redhat.com>
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Date: Wed, 12 Jul 2023 17:46:56 +0200
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Subject: [PATCH 05/37] vfio/pci: Static Resizable BAR capability
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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RH-Author: Cédric Le Goater <clg@redhat.com>
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RH-MergeRequest: 179: vfio: live migration support
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RH-Bugzilla: 2192818
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RH-Acked-by: Eric Auger <eric.auger@redhat.com>
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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RH-Commit: [3/28] 42e9f4b517eb919c77c6fdbe771d9d05a91955bd (clegoate/qemu-kvm-c9s)
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Bugzilla: https://bugzilla.redhat.com/2192818
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commit b5048a4cbfa0
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Author: Alex Williamson <alex.williamson@redhat.com>
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Date: Thu May 4 14:42:48 2023 -0600
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vfio/pci: Static Resizable BAR capability
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The PCI Resizable BAR (ReBAR) capability is currently hidden from the
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VM because the protocol for interacting with the capability does not
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support a mechanism for the device to reject an advertised supported
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BAR size. However, when assigned to a VM, the act of resizing the
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BAR requires adjustment of host resources for the device, which
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absolutely can fail. Linux does not currently allow us to reserve
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resources for the device independent of the current usage.
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The only writable field within the ReBAR capability is the BAR Size
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register. The PCIe spec indicates that when written, the device
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should immediately begin to operate with the provided BAR size. The
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spec however also notes that software must only write values
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corresponding to supported sizes as indicated in the capability and
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control registers. Writing unsupported sizes produces undefined
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results. Therefore, if the hypervisor were to virtualize the
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capability and control registers such that the current size is the
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only indicated available size, then a write of anything other than
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the current size falls into the category of undefined behavior,
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where we can essentially expose the modified ReBAR capability as
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read-only.
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This may seem pointless, but users have reported that virtualizing
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the capability in this way not only allows guest software to expose
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related features as available (even if only cosmetic), but in some
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scenarios can resolve guest driver issues. Additionally, no
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regressions in behavior have been reported for this change.
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A caveat here is that the PCIe spec requires for compatibility that
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devices report support for a size in the range of 1MB to 512GB,
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therefore if the current BAR size falls outside that range we revert
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to hiding the capability.
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Reviewed-by: Cédric Le Goater <clg@redhat.com>
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Link: https://lore.kernel.org/r/20230505232308.2869912-1-alex.williamson@redhat.com
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Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
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Signed-off-by: Cédric Le Goater <clg@redhat.com>
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---
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hw/vfio/pci.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++-
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1 file changed, 53 insertions(+), 1 deletion(-)
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diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
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index 579b92a6ed..6cd3a98c39 100644
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--- a/hw/vfio/pci.c
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+++ b/hw/vfio/pci.c
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@@ -2069,6 +2069,54 @@ static int vfio_add_std_cap(VFIOPCIDevice *vdev, uint8_t pos, Error **errp)
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return 0;
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}
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+static int vfio_setup_rebar_ecap(VFIOPCIDevice *vdev, uint16_t pos)
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+{
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+ uint32_t ctrl;
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+ int i, nbar;
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+
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+ ctrl = pci_get_long(vdev->pdev.config + pos + PCI_REBAR_CTRL);
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+ nbar = (ctrl & PCI_REBAR_CTRL_NBAR_MASK) >> PCI_REBAR_CTRL_NBAR_SHIFT;
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+
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+ for (i = 0; i < nbar; i++) {
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+ uint32_t cap;
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+ int size;
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+
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+ ctrl = pci_get_long(vdev->pdev.config + pos + PCI_REBAR_CTRL + (i * 8));
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+ size = (ctrl & PCI_REBAR_CTRL_BAR_SIZE) >> PCI_REBAR_CTRL_BAR_SHIFT;
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+
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+ /* The cap register reports sizes 1MB to 128TB, with 4 reserved bits */
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+ cap = size <= 27 ? 1U << (size + 4) : 0;
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+
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+ /*
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+ * The PCIe spec (v6.0.1, 7.8.6) requires HW to support at least one
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+ * size in the range 1MB to 512GB. We intend to mask all sizes except
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+ * the one currently enabled in the size field, therefore if it's
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+ * outside the range, hide the whole capability as this virtualization
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+ * trick won't work. If >512GB resizable BARs start to appear, we
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+ * might need an opt-in or reservation scheme in the kernel.
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+ */
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+ if (!(cap & PCI_REBAR_CAP_SIZES)) {
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+ return -EINVAL;
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+ }
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+
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+ /* Hide all sizes reported in the ctrl reg per above requirement. */
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+ ctrl &= (PCI_REBAR_CTRL_BAR_SIZE |
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+ PCI_REBAR_CTRL_NBAR_MASK |
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+ PCI_REBAR_CTRL_BAR_IDX);
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+
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+ /*
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+ * The BAR size field is RW, however we've mangled the capability
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+ * register such that we only report a single size, ie. the current
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+ * BAR size. A write of an unsupported value is undefined, therefore
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+ * the register field is essentially RO.
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+ */
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+ vfio_add_emulated_long(vdev, pos + PCI_REBAR_CAP + (i * 8), cap, ~0);
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+ vfio_add_emulated_long(vdev, pos + PCI_REBAR_CTRL + (i * 8), ctrl, ~0);
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+ }
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+
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+ return 0;
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+}
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+
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static void vfio_add_ext_cap(VFIOPCIDevice *vdev)
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{
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PCIDevice *pdev = &vdev->pdev;
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@@ -2142,9 +2190,13 @@ static void vfio_add_ext_cap(VFIOPCIDevice *vdev)
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case 0: /* kernel masked capability */
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case PCI_EXT_CAP_ID_SRIOV: /* Read-only VF BARs confuse OVMF */
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case PCI_EXT_CAP_ID_ARI: /* XXX Needs next function virtualization */
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- case PCI_EXT_CAP_ID_REBAR: /* Can't expose read-only */
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trace_vfio_add_ext_cap_dropped(vdev->vbasedev.name, cap_id, next);
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break;
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+ case PCI_EXT_CAP_ID_REBAR:
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+ if (!vfio_setup_rebar_ecap(vdev, next)) {
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+ pcie_add_capability(pdev, cap_id, cap_ver, next, size);
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+ }
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+ break;
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default:
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pcie_add_capability(pdev, cap_id, cap_ver, next, size);
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}
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--
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2.39.3
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