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KVM: x86/xen: Don't truncate RAX when handling hypercall from protected guest

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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: b5aead0064 ("KVM: x86: Assume a 64-bit hypercall for guests with protected state")
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://patch.msgid.link/20260529222223.870923-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2026-05-29 15:21:46 -07:00
parent 09912b8ad2
commit 9377016c2f
1 changed files with 3 additions and 3 deletions
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6
arch/x86/kvm/xen.c
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@ -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);