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vmm: Reduce MMIO address space by 4KiB

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In order to workaround a Linux bug that happens when we place devices at
the end of the physical address space on recent hardware (52 bits limit)
we reduce the MMIO address space by one 4k page. This way, nothing gets
allocated in the last 4k of the address space, which is negligible given
the amount of space in the address space.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
This commit is contained in:
Sebastien Boeuf 2020-06-09 13:58:26 +02:00 committed by Rob Bradford
parent 5f0b620148
commit 653087d7a3
1 changed files with 10 additions and 3 deletions
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13
vmm/src/memory_manager.rs
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@ -139,6 +139,13 @@ const LENGTH_OFFSET_HIGH: u64 = 0xC;
const STATUS_OFFSET: u64 = 0x14;
const SELECTION_OFFSET: u64 = 0;
// The MMIO address space size is substracted with the size of a 4k page. This
// is done on purpose to workaround a Linux bug when the VMM allocates devices
// at the end of the addressable space.
fn mmio_address_space_size() -> u64 {
(1 << get_host_cpu_phys_bits()) - 0x1000
}
impl BusDevice for MemoryManager {
fn read(&mut self, _base: u64, offset: u64, data: &mut [u8]) {
if self.selected_slot < self.hotplug_slots.len() {
@ -257,7 +264,7 @@ impl MemoryManager {
let guest_memory =
GuestMemoryMmap::from_arc_regions(mem_regions).map_err(Error::GuestMemory)?;
let end_of_device_area = GuestAddress((1 << get_host_cpu_phys_bits()) - 1);
let end_of_device_area = GuestAddress(mmio_address_space_size() - 1);
let mut start_of_device_area = MemoryManager::start_addr(guest_memory.last_addr(), false);
@ -295,13 +302,13 @@ impl MemoryManager {
hotplug_slots.resize_with(HOTPLUG_COUNT, HotPlugState::default);
#[cfg(target_arch = "x86_64")]
// Let's allocate 64 GiB of addressable MMIO space, starting at 0.
// Both MMIO and PIO address spaces start at address 0.
let allocator = Arc::new(Mutex::new(
SystemAllocator::new(
GuestAddress(0),
1 << 16 as GuestUsize,
GuestAddress(0),
1 << get_host_cpu_phys_bits(),
mmio_address_space_size(),
layout::MEM_32BIT_RESERVED_START,
layout::MEM_32BIT_DEVICES_SIZE,
vec![GsiApic::new(