Although explicitly disallowed by the PCI spec, some guests read a single byte or word from mmio. Likely a guest OS bug, but I have an OS which reads single bytes and it works fine on real hardware.
Signed-off-by: Bernhard Kohl <bernhard.k...@nsn.com> Signed-off-by: Michael S. Tsirkin <m...@redhat.com> --- OK so it could like something like the below. However, my question is: do we need to put this in or can the guest simply be fixed? hw/msix.c | 31 +++++++++++++++++++++++++++---- 1 files changed, 27 insertions(+), 4 deletions(-) diff --git a/hw/msix.c b/hw/msix.c index f66d255..38dff59 100644 --- a/hw/msix.c +++ b/hw/msix.c @@ -102,10 +102,28 @@ static uint32_t msix_mmio_readl(void *opaque, target_phys_addr_t addr) return pci_get_long(page + offset); } -static uint32_t msix_mmio_read_unallowed(void *opaque, target_phys_addr_t addr) + /* Note: + * PCI spec requires that all MSI-X table accesses are either DWORD or QWORD, + * size aligned. Some guests seem to violate this rule for read accesses, + * performing single byte reads. Since it's easy to support this, let's do so. + * Also support 16 bit size aligned reads, just in case. + */ +static uint32_t msix_mmio_readw(void *opaque, target_phys_addr_t addr) { - fprintf(stderr, "MSI-X: only dword read is allowed!\n"); - return 0; + PCIDevice *dev = opaque; + unsigned int offset = addr & (MSIX_PAGE_SIZE - 1) & ~0x1; + void *page = dev->msix_table_page; + + return pci_get_word(page + offset); +} + +static uint32_t msix_mmio_readb(void *opaque, target_phys_addr_t addr) +{ + PCIDevice *dev = opaque; + unsigned int offset = addr & (MSIX_PAGE_SIZE - 1); + void *page = dev->msix_table_page; + + return pci_get_byte(page + offset); } static uint8_t msix_pending_mask(int vector) @@ -192,6 +210,11 @@ static void msix_mmio_writel(void *opaque, target_phys_addr_t addr, msix_handle_mask_update(dev, vector); } +/* PCI spec: + * For all accesses to MSI-X Table and MSI-X PBA fields, software must use + * aligned full DWORD or aligned full QWORD transactions; otherwise, the result + * is undefined. + */ static void msix_mmio_write_unallowed(void *opaque, target_phys_addr_t addr, uint32_t val) { @@ -203,7 +226,7 @@ static CPUWriteMemoryFunc * const msix_mmio_write[] = { }; static CPUReadMemoryFunc * const msix_mmio_read[] = { - msix_mmio_read_unallowed, msix_mmio_read_unallowed, msix_mmio_readl + msix_mmio_readb, msix_mmio_readw, msix_mmio_readl }; /* Should be called from device's map method. */ -- 1.7.3.2.91.g446ac