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KVM: x86: Redefine 'longmode' as a flag for KVM_EXIT_HYPERCALL

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The 'longmode' field is a bit annoying as it blows an entire __u32 to
represent a boolean value. Since other architectures are looking to add
support for KVM_EXIT_HYPERCALL, now is probably a good time to clean it
up.

Redefine the field (and the remaining padding) as a set of flags.
Preserve the existing ABI by using bit 0 to indicate if the guest was in
long mode and requiring that the remaining 31 bits must be zero.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230404154050.2270077-2-oliver.upton@linux.dev
This commit is contained in:
Oliver Upton 2023-04-04 15:40:38 +00:00 • committed by Marc Zyngier
parent e8d018dd02
commit e65733b5c5
5 changed files with 23 additions and 5 deletions
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3
Documentation/virt/kvm/api.rst
View file

@ -6218,8 +6218,7 @@ to the byte array.
__u64 nr;
__u64 args[6];
__u64 ret;
__u32 longmode;
__u32 pad;
__u64 flags;
} hypercall;
Unused. This was once used for 'hypercall to userspace'. To implement

7
arch/x86/include/asm/kvm_host.h
View file

@ -2204,4 +2204,11 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
KVM_X86_QUIRK_FIX_HYPERCALL_INSN | \
KVM_X86_QUIRK_MWAIT_NEVER_UD_FAULTS)
/*
* KVM previously used a u32 field in kvm_run to indicate the hypercall was
* initiated from long mode. KVM now sets bit 0 to indicate long mode, but the
* remaining 31 lower bits must be 0 to preserve ABI.
*/
#define KVM_EXIT_HYPERCALL_MBZ GENMASK_ULL(31, 1)
#endif /* _ASM_X86_KVM_HOST_H */

3
arch/x86/include/uapi/asm/kvm.h
View file

@ -559,4 +559,7 @@ struct kvm_pmu_event_filter {
#define KVM_VCPU_TSC_CTRL 0 /* control group for the timestamp counter (TSC) */
#define KVM_VCPU_TSC_OFFSET 0 /* attribute for the TSC offset */
/* x86-specific KVM_EXIT_HYPERCALL flags. */
#define KVM_EXIT_HYPERCALL_LONG_MODE BIT(0)
#endif /* _ASM_X86_KVM_H */

6
arch/x86/kvm/x86.c
View file

@ -9803,7 +9803,11 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
vcpu->run->hypercall.args[0] = gpa;
vcpu->run->hypercall.args[1] = npages;
vcpu->run->hypercall.args[2] = attrs;
vcpu->run->hypercall.longmode = op_64_bit;
vcpu->run->hypercall.flags = 0;
if (op_64_bit)
vcpu->run->hypercall.flags |= KVM_EXIT_HYPERCALL_LONG_MODE;
WARN_ON_ONCE(vcpu->run->hypercall.flags & KVM_EXIT_HYPERCALL_MBZ);
vcpu->arch.complete_userspace_io = complete_hypercall_exit;
return 0;
}

9
include/uapi/linux/kvm.h
View file

@ -341,8 +341,13 @@ struct kvm_run {
__u64 nr;
__u64 args[6];
__u64 ret;
__u32 longmode;
__u32 pad;
union {
#ifndef __KERNEL__
__u32 longmode;
#endif
__u64 flags;
};
} hypercall;
/* KVM_EXIT_TPR_ACCESS */
struct {