KVM_CREATE_PIT2 #1

evrim · 2017-08-27T04:57:35Z

Hello,

kvm.c<x86> reads:

 133 │ void kvm__arch_init(struct kvm *kvm, const char *hugetlbfs_path, u64 ram_size)                                         
 134 │ {                                                                                                                      
 135 │     struct kvm_pit_config pit_config = { .flags = 0, };                                                                
 136 │     int ret;                                                                                                           
 137 │                                                                                                                        
 138 │     ret = ioctl(kvm->vm_fd, KVM_SET_TSS_ADDR, 0xfffbd000);                                                             
 139 │     if (ret < 0)                                                                                                       
 140 │         die_perror("KVM_SET_TSS_ADDR ioctl");                                                                          
 141 │                                                                                                                        
 142 │     ret = ioctl(kvm->vm_fd, KVM_CREATE_PIT2, &pit_config);                                                             
 143 │     if (ret < 0)                                                                                                       
 144 │         die_perror("KVM_CREATE_PIT2 ioctl");                                                                           
 145 │                                                                                                                        
 146 │     if (ram_size < KVM_32BIT_GAP_START) {                                                                              
 147 │         kvm->ram_size = ram_size;                                                                                      
 148 │         kvm->ram_start = mmap_anon_or_hugetlbfs(kvm, hugetlbfs_path, ram_size);                                        
 149 │     } else {                                                                                                           
 150 │         kvm->ram_start = mmap_anon_or_hugetlbfs(kvm, hugetlbfs_path, ram_size + KVM_32BIT_GAP_SIZE);                   
 151 │         kvm->ram_size = ram_size + KVM_32BIT_GAP_SIZE;                                                                 
 152 │         if (kvm->ram_start != MAP_FAILED)                                                                              
 153 │             /*                                                                                                         
 154 │              * We mprotect the gap (see kvm__init_ram() for details) PROT_NONE so that                                 
 155 │              * if we accidently write to it, we will know.                                                             
 156 │              */                                                                                                        
 157 │             mprotect(kvm->ram_start + KVM_32BIT_GAP_START, KVM_32BIT_GAP_SIZE, PROT_NONE);                             
 158 │     }                                                                                                                  
 159 │     if (kvm->ram_start == MAP_FAILED)                                                                                  
 160 │         die("out of memory");                                                                                          
 161 │                                                                                                                        
 162 │     madvise(kvm->ram_start, kvm->ram_size, MADV_MERGEABLE);                                                            
 163 │                                                                                                                        
 164 │     ret = ioctl(kvm->vm_fd, KVM_CREATE_IRQCHIP);                                                                       
 165 │     if (ret < 0)                                                                                                       
 166 │         die_perror("KVM_CREATE_IRQCHIP ioctl");                                                                        
 167 │ }

Interestingly, kernel Documentation/virtual/kvm/api.txt reads:

Capability: KVM_CAP_PIT2
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_pit_config (in)
Returns: 0 on success, -1 on error

Creates an in-kernel device model for the i8254 PIT. This call is only valid
after enabling in-kernel irqchip support via KVM_CREATE_IRQCHIP. The following
parameters have to be passed:

Question: should CREATE_PIT2 be executed after CREATE_IRQCHIP in line 164?

best,
evrim.

Linux, besides CPIO, supports 7 different compressed formats for the initrd (gzip, bzip2, LZMA, XZ, LZO, LZ4, ZSTD), but kvmtool only recognizes one of them. Remove the initrd magic check because: 1. It doesn't bring much to the end user, as the Linux kernel still complains if the initrd is in an unknown format. 2. --kernel can be used to load something that is not a Linux kernel (like a kvm-unit-tests test), in which case a format which is not supported by a Linux kernel can still be perfectly valid. For example, kvm-unit-tests load the test environment as an initrd in plain ASCII format. 3. It cuts down on the maintenance effort when new formats are added to the Linux kernel. Not a big deal, since that doesn't happen very often, but it's still an effort with very little gain (see point #1 above). Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> Link: https://lore.kernel.org/r/20220214165830.69207-2-alexandru.elisei@arm.com Signed-off-by: Will Deacon <will@kernel.org>

bjackman · 2024-04-15T15:30:45Z

Looks like since this commit the CREATE_PIT2 command fails in practice.

If I just reorder the ioctls in kvm__arch_init it seems to work

bjackman · 2024-04-15T15:44:27Z

I sent a patch - https://lore.kernel.org/kvm/20240415154244.2840081-1-jackmanb@google.com/T/#u

bjackman · 2024-04-19T14:23:02Z

This is now fixed by e73a6b2

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