Commit 0e5c9a9d authored by Marc Zyngier's avatar Marc Zyngier
Browse files

KVM: arm64: Expose SMC/HVC width to userspace 



When returning to userspace to handle a SMCCC call, we consistently
set PC to point to the instruction immediately after the HVC/SMC.

However, should userspace need to know the exact address of the
trapping instruction, it needs to know about the *size* of that
instruction. For AArch64, this is pretty easy. For AArch32, this
is a bit more funky, as Thumb has 16bit encodings for both HVC
and SMC.

Expose this to userspace with a new flag that directly derives
from ESR_EL2.IL. Also update the documentation to reflect the PC
state at the point of exit.

Finally, this fixes a small buglet where the hypercall.{args,ret}
fields would not be cleared on exit, and could contain some
random junk.

Reviewed-by: default avatarOliver Upton <oliver.upton@linux.dev>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/86pm8iv8tj.wl-maz@kernel.org
parent 60e7dade

Documentation/virt/kvm/api.rst

+8 −0
Original line number Diff line number Diff line
@@ -6244,6 +6244,14 @@ Definition of ``flags``: 
   conduit to initiate the SMCCC call. If this bit is 0 then the guest

   used the HVC conduit for the SMCCC call.



 - ``KVM_HYPERCALL_EXIT_16BIT``: Indicates that the guest used a 16bit

   instruction to initiate the SMCCC call. If this bit is 0 then the

   guest used a 32bit instruction. An AArch64 guest always has this

   bit set to 0.



At the point of exit, PC points to the instruction immediately following

the trapping instruction.



::



		/* KVM_EXIT_TPR_ACCESS */

arch/arm64/include/uapi/asm/kvm.h

+2 −1
Original line number Diff line number Diff line
@@ -492,6 +492,7 @@ struct kvm_smccc_filter { 


/* arm64-specific KVM_EXIT_HYPERCALL flags */

#define KVM_HYPERCALL_EXIT_SMC		(1U << 0)

#define KVM_HYPERCALL_EXIT_16BIT	(1U << 1)



#endif

arch/arm64/kvm/hypercalls.c

+11 −5
Original line number Diff line number Diff line
@@ -222,13 +222,19 @@ static void kvm_prepare_hypercall_exit(struct kvm_vcpu *vcpu, u32 func_id) 
{

	u8 ec = ESR_ELx_EC(kvm_vcpu_get_esr(vcpu));

	struct kvm_run *run = vcpu->run;



	run->exit_reason = KVM_EXIT_HYPERCALL;

	run->hypercall.nr = func_id;

	run->hypercall.flags = 0;

	u64 flags = 0;



	if (ec == ESR_ELx_EC_SMC32 || ec == ESR_ELx_EC_SMC64)

		run->hypercall.flags |= KVM_HYPERCALL_EXIT_SMC;

		flags |= KVM_HYPERCALL_EXIT_SMC;



	if (!kvm_vcpu_trap_il_is32bit(vcpu))

		flags |= KVM_HYPERCALL_EXIT_16BIT;



	run->exit_reason = KVM_EXIT_HYPERCALL;

	run->hypercall = (typeof(run->hypercall)) {

		.nr	= func_id,

		.flags	= flags,

	};

}



int kvm_smccc_call_handler(struct kvm_vcpu *vcpu)