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KVM: arm64: Expose SMC/HVC width to userspace

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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: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/86pm8iv8tj.wl-maz@kernel.org
This commit is contained in:
Marc Zyngier 2023-04-05 12:48:58 +01:00
parent 60e7dade49
commit 0e5c9a9d65
3 changed files with 21 additions and 6 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

8
Documentation/virt/kvm/api.rst
View file

@ -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 */

3
arch/arm64/include/uapi/asm/kvm.h
View file

@ -491,7 +491,8 @@ struct kvm_smccc_filter {
};
/* arm64-specific KVM_EXIT_HYPERCALL flags */
#define KVM_HYPERCALL_EXIT_SMC (1U << 0)
#define KVM_HYPERCALL_EXIT_SMC (1U << 0)
#define KVM_HYPERCALL_EXIT_16BIT (1U << 1)
#endif

16
arch/arm64/kvm/hypercalls.c
View file

@ -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)