From: Sean Christopherson Date: Fri, 29 May 2026 22:21:46 +0000 (-0700) Subject: KVM: x86/xen: Don't truncate RAX when handling hypercall from protected guest X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9377016c2f9e2e25dca5788ac109190daf116134;p=thirdparty%2Fkernel%2Flinux.git KVM: x86/xen: Don't truncate RAX when handling hypercall from protected guest Don't truncate RAX when handling a Xen hypercall for a guest with protected state, as KVM's ABI is to assume the guest is in 64-bit for such cases (the guest leaving garbage in 63:32 after a transition to 32-bit mode is far less likely than 63:32 being necessary to complete the hypercall). Fixes: b5aead0064f3 ("KVM: x86: Assume a 64-bit hypercall for guests with protected state") Reviewed-by: David Woodhouse Link: https://patch.msgid.link/20260529222223.870923-4-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index 6d9be74bb673..895095dc684e 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1678,15 +1678,14 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu) bool handled = false; u8 cpl; - input = (u64)kvm_register_read(vcpu, VCPU_REGS_RAX); - /* Hyper-V hypercalls get bit 31 set in EAX */ - if ((input & 0x80000000) && + if ((kvm_rax_read(vcpu) & 0x80000000) && kvm_hv_hypercall_enabled(vcpu)) return kvm_hv_hypercall(vcpu); longmode = is_64_bit_hypercall(vcpu); if (!longmode) { + input = (u32)kvm_rax_read(vcpu); params[0] = (u32)kvm_rbx_read(vcpu); params[1] = (u32)kvm_rcx_read(vcpu); params[2] = (u32)kvm_rdx_read(vcpu); @@ -1696,6 +1695,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu) } else { #ifdef CONFIG_X86_64 + input = (u64)kvm_rax_read(vcpu); params[0] = (u64)kvm_rdi_read(vcpu); params[1] = (u64)kvm_rsi_read(vcpu); params[2] = (u64)kvm_rdx_read(vcpu);