Pkg xen devel - Mar 2022 - Bug#988333: Bug#988333: Bug#988333: libxenmisc4.16: libxl fails to grant necessary I/O memory access for gfx_passthru of Intel IGD

On 3/8/2022 6:00 AM, Hans van Kranenburg wrote:
>> On 3/7/22 18:30, Chuck Zmudzinski wrote:
>>> [...]
>>
>> Thanks for adding all the info and researching this, Chuck!
>>
>> Hans
>
> Thanks for the encouragement. Now I am working on two things:
>
> 1. I want to understand the problem better so I can Improve the patch. 
> The patch I proposed for this bug currently adds two pages to the 
> permitted I/O addresses for the domain starting at 0xcc490, but I 
> don't know the best way to determine that memory address. Probably a 
> hard-coded constant address is not good enough to handle all possible 
> hardware affected by this bug. It might be different for different 
> Intel revisions of the Intel IGD, and it probably can be read from 
> somewhere, but where? Also, what is that memory for? I would like to 
> understand that before finalizing what the patch should be. I am 
> researching these things, and then I will have a better version of the 
> patch to propose for Xen upstream. I have found places where Qemu/vfio 
> deals with what they call Intel IGD quirks, and that information can 
> shed light on how to solve this bug in Xen. Hopefully upstream will 
> accept a patch when we have a patch to propose to them. I am fairly 
> sure there really is a bug that should be patched upstream to improve 
> support for the Intel IGD passthrough feature on Xen.
I discovered that address 0xcc490 is for the Intel IGD Opregion, an area 
of memory that Xen's hvmloader and Qemu both know about. So I was able 
to propose this patch to the xen-devel mailing list.

Regards,

Chuck

--- a/tools/libs/light/libxl_pci.c
+++ b/tools/libs/light/libxl_pci.c
@@ -24,6 +24,7 @@
 ?#define PCI_OPTIONS??????????? "msitranslate=%d,power_mgmt=%d"
 ?#define PCI_BDF_XSPATH???????? "%04x-%02x-%02x-%01x"
 ?#define PCI_PT_QDEV_ID???????? "pci-pt-%02x_%02x.%01x"
+#define PCI_INTEL_OPREGION???? 0xfc /* value defined in 
tools/firmware/hvmloader/pci_regs.h */

 ?static unsigned int pci_encode_bdf(libxl_device_pci *pci)
 ?{
@@ -640,6 +641,45 @@
 ?}

 ?/*
+ * This function assumes prior verification
+ * that pci is an Intel IGD device.
+ */
+static uint32_t sysfs_dev_get_igd_opregion(libxl__gc *gc, 
libxl_device_pci *pci)
+{
+??? char *pci_device_vendor_path +???????????
GCSPRINTF(SYSFS_PCI_DEV"/"PCI_BDF"/config",
+????????????????????? pci->domain, pci->bus, pci->dev, pci->func);
+??? size_t read_item;
+??? uint32_t igd_opregion;
+
+??? FILE *f = fopen(pci_device_vendor_path, "r");
+??? if (!f) {
+??????? LOGE(ERROR,
+???????????? "pci device "PCI_BDF" does not have config
attribute",
+???????????? pci->domain, pci->bus, pci->dev, pci->func);
+??????? return 0xffffffff;
+??? }
+??? if (fseek(f, PCI_INTEL_OPREGION, SEEK_SET)) {
+??????? LOGE(ERROR,
+???????????? "pci device "PCI_BDF": cannot find igd-opregion
address",
+???????????? pci->domain, pci->bus, pci->dev, pci->func);
+??????? fclose(f);
+??????? return 0xffffffff;
+??? }
+??? read_item = fread(&igd_opregion, 4, 1, f);
+??? fclose(f);
+
+??? if (read_item != 1) {
+??????? LOGE(ERROR,
+???????????? "cannot read igd-opresgion address of pci device
"PCI_BDF,
+???????????? pci->domain, pci->bus, pci->dev, pci->func);
+??????? return 0xffffffff;
+??? }
+
+??? return igd_opregion;
+}
+
+/*
 ? * A brief comment about slots.? I don't know what slots are for; however,
 ? * I have by experimentation determined:
 ? * - Before a device can be bound to pciback, its BDF must first be listed
@@ -2531,6 +2571,34 @@
 ?????????????????? domid, vga_iomem_start, (vga_iomem_start + 0x20 - 1));
 ???????????? return ret;
 ???????? }
+
+??????? /* Allow access to Intel igd-opregion */
+??????? if (sysfs_dev_get_vendor(gc, pci) == 0x8086)
+??????? {
+??????????? uint32_t igd_opregion = sysfs_dev_get_igd_opregion(gc, pci);
+??????????? if (igd_opregion == 0xffffffff)
+??????????????? break;
+??????????? vga_iomem_start = ((uint64_t)igd_opregion) >> XC_PAGE_SHIFT;
+??????????? ret = xc_domain_iomem_permission(CTX->xch, stubdom_domid,
+???????????????????????????????????????????? vga_iomem_start, 0x2, 1);
+??????????? if (ret < 0) {
+??????????????? LOGED(ERROR, domid,
+????????????????????? "failed to give stubdom%d access to iomem range
"
+????????????????????? "%"PRIx64"-%"PRIx64" for IGD
passthru",
+????????????????????? stubdom_domid,
+????????????????????? vga_iomem_start, (vga_iomem_start + 0x2 - 1));
+??????????????? return ret;
+??????????? }
+??????????? ret = xc_domain_iomem_permission(CTX->xch, domid,
+???????????????????????????????????????????? vga_iomem_start, 0x2, 1);
+??????????? if (ret < 0) {
+??????????????? LOGED(ERROR, domid,
+????????????????????? "failed to give dom%d access to iomem range "
+????????????????????? "%"PRIx64"-%"PRIx64" for IGD
passthru",
+????????????????????? domid, vga_iomem_start, (vga_iomem_start + 0x2 - 1));
+??????????????? return ret;
+??????????? }
+??????? }
 ???????? break;
 ???? }

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