Messages in this thread | | | Date | Mon, 13 Dec 2021 10:24:08 +0100 | Subject | Re: [PATCH 16/19] kvm: x86: Introduce KVM_{G|S}ET_XSAVE2 ioctl | From | Paolo Bonzini <> |
| |
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
| |