How to guarantee all DMA data write into ram when getting msi interrupt?

There are some questions that make me confused:

1. Msi interrupt is a memory write request. Can msi ensure that all DMA data have been written into ram? or only ensure that the data has been transferred completely on pci bridge?

2. If msi interrupt only ensures the data transfer completely on pci bridge. How to guarantee all DMA data write into ram when getting msi interrupt?

3. Does msi memory write request really write into ram?

Thanks in advance.