On 11/13/23 08:32, Vivek Kasireddy wrote: > A recent OVMF update has resulted in MMIO regions being placed at > the upper end of the physical address space. As a result, when a > Host device is passthrough'd 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: Laszlo Ersek <ler...@redhat.com> > Cc: Dongwon Kim <dongwon....@intel.com> > Signed-off-by: Vivek Kasireddy <vivek.kasire...@intel.com> > --- > 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..8326ec95bc 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 is passthroughing any devices via VFIO. We don't > + * have to limit phys_bits if there are no valid passthrough 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; > + if (!warned2) { > + warn_report("Using physical bits (%u)" > + " to prevent VFIO mapping failures", > + iommu_phys_bits); > + warned2 = true; > + } > + } > + > return phys_bits; > } >
I only have very superficial comments here (sorry about that -- I find it too bad that this QEMU source file seems to have no designated reviewer or maintainer in QEMU, so I don't want to ignore it). - Terminology: I think we like to call these devices "assigned", and not "passed through". Also, in noun form, "device assignment" and not "device passthrough". Sorry about being pedantic. - As I (may have) mentioned in my OVMF comments, I'm unsure if narrowing the VCPU "phys address bits" property due to host IOMMU limitations is a good design. To me it feels like hacking one piece of information into another (unrelated) piece of information. It vaguely makes me think we're going to regret this later. But I don't have any specific, current counter-argument, admittedly. Laszlo
