KVM_32BIT_GAP #2

evrim · 2017-08-27T05:18:14Z

Hello,

kvm.c<x86> reads:

  80 │ /*                                                                                                                     
  81 │  * Allocating RAM size bigger than 4GB requires us to leave a gap                                                      
  82 │  * in the RAM which is used for PCI MMIO, hotplug, and unconfigured                                                    
  83 │  * devices (see documentation of e820_setup_gap() for details).                                                        
  84 │  *                                                                                                                     
  85 │  * If we're required to initialize RAM bigger than 4GB, we will create                                                 
  86 │  * a gap between 0xe0000000 and 0x100000000 in the guest virtual mem space.                                            
  87 │  */
  88 │ 
  89 │ void kvm__init_ram(struct kvm *kvm)                                                                                    
  90 │ {                                                                                                                      
  91 │     u64 phys_start, phys_size;                                                                                         
  92 │     void    *host_mem;

kvm-arch.h<x86> reads:

   9 │ 
  10 │ /*                                                                                                                     
  11 │  * The hole includes VESA framebuffer and PCI memory.                                                                  
  12 │  */
  13 │ #define KVM_32BIT_MAX_MEM_SIZE  (1ULL << 32)                                      
  14 │ #define KVM_32BIT_GAP_SIZE  (768 << 20)                                       
  15 │ #define KVM_32BIT_GAP_START (KVM_32BIT_MAX_MEM_SIZE - KVM_32BIT_GAP_SIZE) 
  17 │ #define KVM_MMIO_START      KVM_32BIT_GAP_START

Gdb tells:

(gdb) p/x (1ULL << 32) - (768 << 20)
$1 = 0xd0000000

confused ⭕️

best,
evrim.

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KVM_32BIT_GAP #2

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