Hi Alex, Eric, > > > Recent updates in OVMF and Seabios have resulted in MMIO regions > > > being placed at the upper end of the physical address space. As a > > > result, when a Host device is assigned to the Guest via VFIO, the > > > following mapping failures occur when VFIO tries to map the MMIO > > > regions of the device: > > > VFIO_MAP_DMA failed: Invalid argument > > > vfio_dma_map(0x557b2f2736d0, 0x380000000000, 0x1000000, > 0x7f98ac400000) = -22 (Invalid argument) > > > > > > The above failures are mainly seen on some Intel platforms where > > > the physical address width is larger than the Host's IOMMU > > > address width. In these cases, VFIO fails to map the MMIO regions > > > because the IOVAs would be larger than the IOMMU aperture regions. > > > > > > Therefore, one way to solve this problem would be to ensure that > > > cpu->phys_bits = <IOMMU phys_bits> > > > This can be done by parsing the IOMMU caps value from sysfs and > > > extracting the address width and using it to override the > > > phys_bits value as shown in this patch. > > > > > > Previous attempt at solving this issue in OVMF: > > > https://edk2.groups.io/g/devel/topic/102359124 > > > > > > Cc: Gerd Hoffmann <kra...@redhat.com> > > > Cc: Philippe Mathieu-Daudé <phi...@linaro.org> > > > Cc: Alex Williamson <alex.william...@redhat.com> > > > Cc: Cédric Le Goater <c...@redhat.com> > > > Cc: Laszlo Ersek <ler...@redhat.com> > > > Cc: Dongwon Kim <dongwon....@intel.com> > > > Acked-by: Gerd Hoffmann <kra...@redhat.com> > > > Tested-by: Yanghang Liu <yangh...@redhat.com> > > > Signed-off-by: Vivek Kasireddy <vivek.kasire...@intel.com> > > > > > > --- > > > v2: > > > - Replace the term passthrough with assigned (Laszlo) > > > - Update the commit message to note that both OVMF and Seabios > > > guests are affected (Cédric) > > > - Update the subject to indicate what is done in the patch > > > --- > > > target/i386/host-cpu.c | 61 > +++++++++++++++++++++++++++++++++++++++++- > > > 1 file changed, 60 insertions(+), 1 deletion(-) > > > > > > diff --git a/target/i386/host-cpu.c b/target/i386/host-cpu.c > > > index 92ecb7254b..5c9fcd7dc2 100644 > > > --- a/target/i386/host-cpu.c > > > +++ b/target/i386/host-cpu.c > > > @@ -12,6 +12,8 @@ > > > #include "host-cpu.h" > > > #include "qapi/error.h" > > > #include "qemu/error-report.h" > > > +#include "qemu/config-file.h" > > > +#include "qemu/option.h" > > > #include "sysemu/sysemu.h" > > > > > > /* Note: Only safe for use on x86(-64) hosts */ > > > @@ -51,11 +53,58 @@ static void host_cpu_enable_cpu_pm(X86CPU > *cpu) > > > env->features[FEAT_1_ECX] |= CPUID_EXT_MONITOR; > > > } > > > > > > +static int intel_iommu_check(void *opaque, QemuOpts *opts, Error > **errp) > > > +{ > > > + g_autofree char *dev_path = NULL, *iommu_path = NULL, *caps = > NULL; > > > + const char *driver = qemu_opt_get(opts, "driver"); > > > + const char *device = qemu_opt_get(opts, "host"); > > > + uint32_t *iommu_phys_bits = opaque; > > > + struct stat st; > > > + uint64_t iommu_caps; > > > + > > > + /* > > > + * Check if the user requested VFIO device assignment. We don't have > > > + * to limit phys_bits if there are no valid assigned devices. > > > + */ > > > + if (g_strcmp0(driver, "vfio-pci") || !device) { > > > + return 0; > > > + } > > > + > > > + dev_path = g_strdup_printf("/sys/bus/pci/devices/%s", device); > > > + if (stat(dev_path, &st) < 0) { > > > + return 0; > > > + } > > > + > > > + iommu_path = g_strdup_printf("%s/iommu/intel-iommu/cap", > dev_path); > > > + if (stat(iommu_path, &st) < 0) { > > > + return 0; > > > + } > > > + > > > + if (g_file_get_contents(iommu_path, &caps, NULL, NULL)) { > > > + if (sscanf(caps, "%lx", &iommu_caps) != 1) { > > > + return 0; > > > + } > > > + *iommu_phys_bits = ((iommu_caps >> 16) & 0x3f) + 1; > > > + } > > > + > > > + return 0; > > > +} > > > + > > > +static uint32_t host_iommu_phys_bits(void) > > > +{ > > > + uint32_t iommu_phys_bits = 0; > > > + > > > + qemu_opts_foreach(qemu_find_opts("device"), > > > + intel_iommu_check, &iommu_phys_bits, NULL); > > > + return iommu_phys_bits; > > > +} > > > + > > > static uint32_t host_cpu_adjust_phys_bits(X86CPU *cpu) > > > { > > > uint32_t host_phys_bits = host_cpu_phys_bits(); > > > + uint32_t iommu_phys_bits = host_iommu_phys_bits(); > > > uint32_t phys_bits = cpu->phys_bits; > > > - static bool warned; > > > + static bool warned, warned2; > > > > > > /* > > > * Print a warning if the user set it to a value that's not the > > > @@ -78,6 +127,16 @@ static uint32_t > host_cpu_adjust_phys_bits(X86CPU *cpu) > > > } > > > } > > > > > > + if (iommu_phys_bits && phys_bits > iommu_phys_bits) { > > > + phys_bits = iommu_phys_bits; > > are you allowed to change the host cpu characteristics without taking > > care of compats for migration? > > Not only is migration an issue, but so is hotplug. Anything that > aligns the VM configuration to the host is going to have migration > issues and anything that does so conditionally based on the current set > of attached devices will have hotplug issues. > > It'd be more prudent to find the least common denominator under > /sys/class/iommu/dmar*/intel-iommu/cap regardless of attached devices, > but it still affects migration compatibility between hosts. > > Also note that vfio-pci can specify the device with either host= or > sysfsdev= and with vfio cdev support and iommufd the file descriptor > for the vfio device might be passed via SCM rights, so we may not have > a reference to it in sysfs. The above appears to only work with the > host= device specification. Thanks, To address both migration and hotplug use-cases, the only option I can see is to just hardcode phys_bits to 39 (smallest iommu aw seen on recent Intel h/w) if an Intel iommu is detected. Or, instead of doing this automatically with this patch, I am thinking of just printing a warning that, in order to prevent VFIO mapping failures, the user needs to add the following when an Intel iommu is detected while launching Qemu: -cpu host,host-phys-bits=on,host-phys-bits-limit=39
Since neither of these options are great, I am wondering if there is a more elegant way to solve this problem that you can recommend. Thanks, Vivek > > Alex
