On Wed, Apr 07, 2021 at 11:29:26PM +0200, Siddharth Chandrasekaran wrote: > Hyper-V supports the use of XMM registers to perform fast hypercalls. > This allows guests to take advantage of the improved performance of the > fast hypercall interface even though a hypercall may require more than > (the current maximum of) two general purpose registers. > > The XMM fast hypercall interface uses an additional six XMM registers > (XMM0 to XMM5) to allow the caller to pass an input parameter block of > up to 112 bytes. Hyper-V can also return data back to the guest in the > remaining XMM registers that are not used by the current hypercall. > > Although the Hyper-v TLFS mentions that a guest cannot use this feature > unless the hypervisor advertises support for it, some hypercalls which > we plan on upstreaming in future uses them anyway. No, please don't do this. Check the feature bit(s) before you issue hypercalls which rely on the extended interface. Wei.
