On 12/13/21 09:23, Wang, Wei W wrote:
On Saturday, December 11, 2021 6:13 AM, Paolo Bonzini wrote:
By the way, I think KVM_SET_XSAVE2 is not needed. Instead:
- KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) should return the size of the
buffer that is passed to KVM_GET_XSAVE2
- KVM_GET_XSAVE2 should fill in the buffer expecting that its size is
whatever KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2) passes
- KVM_SET_XSAVE can just expect a buffer that is bigger than 4k if the
save states recorded in the header point to offsets larger than 4k.
I think one issue is that KVM_SET_XSAVE works with "struct kvm_xsave" (hardcoded 4KB buffer),
including kvm_vcpu_ioctl_x86_set_xsave. The states obtained via KVM_GET_XSAVE2 will be made
using "struct kvm_xsave2".
Did you mean that we could add a new code path under KVM_SET_XSAVE to make it work with
the new "struct kvm_xsave2"?
There is no need for struct kvm_xsave2, because there is no need for a
"size" argument.
- KVM_GET_XSAVE2 *is* needed, and it can expect a buffer as big as the
return value of KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2)
- but KVM_SET_XSAVE2 is not needed, because KVM_SET_XSAVE can use
copy_from_user to read the XSTATE_BV, use it to deduce the size of the
buffer, and use copy_from_user to read the full size of the buffer.
For this to work you can redefine struct kvm_xsave to
struct kvm_xsave {
__u32 region[1024];
/*
* KVM_GET_XSAVE only uses 4096 bytes and only returns
* user save states up to save state 17 (TILECFG).
*
* For KVM_GET_XSAVE2, the total size of region + extra
* must be the size that is communicated by
* KVM_CHECK_EXTENSION(KVM_CAP_XSAVE2).
*
* KVM_SET_XSAVE uses the extra field if the struct was
* returned by KVM_GET_XSAVE2.
*/
__u32 extra[];
}
Paolo
