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[Qemu-devel] [RFC] Virt machine memory map

From: Pavel Fedin
Subject: [Qemu-devel] [RFC] Virt machine memory map
Date: Mon, 20 Jul 2015 11:55:00 +0300


 In our project we work on a very fast paravirtualized network I/O drivers, 
based  on ivshmem. We
successfully got ivshmem working on ARM, however with one hack.
Currently we have:
--- cut ---
    [VIRT_PCIE_MMIO] =          { 0x10000000, 0x2eff0000 },
    [VIRT_PCIE_PIO] =           { 0x3eff0000, 0x00010000 },
    [VIRT_PCIE_ECAM] =          { 0x3f000000, 0x01000000 },
    [VIRT_MEM] =                { 0x40000000, 30ULL * 1024 * 1024 * 1024 },
--- cut ---
 And MMIO region is not enough for us because we want to have 1GB mapping for 
PCI device. In order
to make it working, we modify the map as follows:
--- cut ---
    [VIRT_PCIE_MMIO] =            { 0x10000000, 0x7eff0000 },
    [VIRT_PCIE_PIO] =           { 0x8eff0000, 0x00010000 },
    [VIRT_PCIE_ECAM] =          { 0x8f000000, 0x01000000 },
    [VIRT_MEM] =             { 0x90000000, 30ULL * 1024 * 1024 * 1024 },
--- cut ---
 The question is - how could we upstream this? I believe modifying 32-bit virt 
memory map this way
is not good. Will it be OK to have different memory map for 64-bit virt ?
 Another possible approach is not to use PCI, but MMIO instead, and just 
specify our region in the
device tree. This way we work around the limitation of having only a single PCI 
MMIO region, and we
could happily place our 1GB device after system RAM.
 Any opinions ?

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia

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