Peter Maydell <peter.maydell@xxxxxxxxxx> writes: > On 1 September 2012 13:28, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote: >> Rusty Russell (8): >> KVM: ARM: Fix walk_msrs() >> KVM: Move KVM_SET_ONE_REG/KVM_GET_ONE_REG to generic code. >> KVM: Add KVM_REG_SIZE() helper. >> KVM: ARM: use KVM_SET_ONE_REG/KVM_GET_ONE_REG. >> KVM: Add KVM_VCPU_GET_REG_LIST. >> KVM: ARM: Use KVM_VCPU_GET_REG_LIST. >> KVM: ARM: Access all registers via KVM_GET_ONE_REG/KVM_SET_ONE_REG. >> KVM ARM: Update api.txt > > So I was thinking about this, and I remembered that the SET_ONE_REG/ > GET_ONE_REG API has userspace pass a pointer to the variable the > kernel should read/write (unlike the _MSR x86 ioctls, where the > actual data value is sent back and forth in the struct). Further, > the kernel only writes a data value of the size of the register > (rather than always reading/writing a uint64_t). > > This is a problem because it means userspace needs to know the > size of each register, and the kernel doesn't provide any way > to determine the size. This defeats the idea that userspace should > be able to migrate kernel register state without having to know > the semantics of all the registers involved. It's there. There are bits in the id which indicate the size: #define KVM_REG_SIZE_SHIFT 52 #define KVM_REG_SIZE_MASK 0x00f0000000000000ULL #define KVM_REG_SIZE_U8 0x0000000000000000ULL #define KVM_REG_SIZE_U16 0x0010000000000000ULL #define KVM_REG_SIZE_U32 0x0020000000000000ULL #define KVM_REG_SIZE_U64 0x0030000000000000ULL #define KVM_REG_SIZE_U128 0x0040000000000000ULL #define KVM_REG_SIZE_U256 0x0050000000000000ULL #define KVM_REG_SIZE_U512 0x0060000000000000ULL #define KVM_REG_SIZE_U1024 0x0070000000000000ULL And my patches added a helper: #define KVM_REG_SIZE(id) \ (1U << (((id) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT)) > I could live with "always read/write 64 bits". I definitely don't > want to have to deal with matching up register widths to accesses > in userspace, please. I changed my mind about the old scheme when I realized we have to deal with 128-bit FPU registers. Cheers, Rusty. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
