Otherwise there would be an ambiguity problem. Suppose that: 1. There is a region from [0x40000, 0x50000) with mmap offset 0x500000. 2. There is a region from [0x48000, 0x58000) with mmap offset 0xA00000. A request has address 0x44000. Which mmap offset should be used? This problem appears with both guest and user addresses. Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com> --- docs/interop/vhost-user.rst | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst index 137c9f3669..8c122c9d21 100644 --- a/docs/interop/vhost-user.rst +++ b/docs/interop/vhost-user.rst @@ -204,6 +204,18 @@ fields at the end. :domid: a 32-bit Xen hypervisor specific domain id. +For all memory regions active at a given time: + +- ``[guest address, guest address + size)`` of one memory region never overlaps + the ``[guest address, guest address + size)`` of another memory region. + +- ``[user address, user address + size)`` of one memory region never overlaps + the ``[user address, user address + size)`` of another memory region. + +Violating any of these is a bug in the front-end. This ensures that a guest +address or user address always refers to at most one location in memory. +The front-end must remove a region before it can add an overlapping one. + Single memory region description ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -672,6 +684,15 @@ The front-end sends a list of vhost memory regions to the back-end using the ``VHOST_USER_SET_MEM_TABLE`` message. Each region has two base addresses: a guest address and a user address. +Memory regions can be added via the ``VHOST_USER_ADD_MEM_REG`` message. They +can be removed via the ``VHOST_USER_REM_MEM_REG`` message. These messages can +only be used if the ``VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS`` protocol +feature has been successfully negotiated. + +Guest addresses are physical addresses in the guest. User addresses are +arbitrary opaque values, though they typically refer to userspace addresses in +the client process. + Messages contain guest addresses and/or user addresses to reference locations within the shared memory. The mapping of these addresses works as follows. --- base-commit: f5a2438405d4ae8b62de7c9b39fac0b2155ee544 change-id: 20260522-vhost-user-dev-aa76e3955555 Best regards, -- Demi Marie Obenour <demiobenour@gmail.com>