The reason we want to skip flatview_simplify() is to prevent unnecessary IOVA address range mapping from being unmapped.
The actual situation we encountered is: When assign EHCI device to the virtual machine, after initializing EHCI in seabios, it will continuously send dma cycles.And EHCI dma buffer is allocated from the range 0xd9000-0xexxxx belonging to zonelow. But in seabios, make_bios_readonly_intel() will modify the attributes in the range of 0xc0000-0x100000,except for the zonelow range. Before these ranges attributes are not changed,qemu will perform flatview_simplify(),and the actual address range formed in flatview is 0xc0000-0xbfffffff.When the properties of this large range are modified to readonly,qemu will unmap all the IOVA mappings in the address range 0xc0000-0xbfffffff. But EHCI device still send dma cycle. So dma cycles of the EHCI device will be blocked by the IOMMU. And we want to skip flatview_simplify(). Error log when starting the virtual machine: DMAR: [DMA Read] Request device [00:10.7] fault addr eb000 [fault reason 06] PTE Read access is not set DMAR: [DMA Read] Request device [00:10.7] fault addr eb000 [fault reason 06] PTE Read access is not set FelixCuioc (1): Skip flatview_simplify() for specific cpu vendor softmmu/memory.c | 16 +++++++++++++++- target/i386/cpu.c | 8 ++++++++ target/i386/cpu.h | 3 +++ 3 files changed, 26 insertions(+), 1 deletion(-) -- 2.17.1
