Hi Marc,
On 2021/6/1 19:44, Marc Zyngier wrote:
Hi Zenghui,
Thanks for having a go at the backport.
On Tue, 01 Jun 2021 12:12:37 +0100,
Zenghui Yu <yuzenghui@xxxxxxxxxx> wrote:
From: Marc Zyngier <maz@xxxxxxxxxx>
commit 26778aaa134a9aefdf5dbaad904054d7be9d656d upstream.
KVM currently updates PC (and the corresponding exception state)
using a two phase approach: first by setting a set of flags,
then by converting these flags into a state update when the vcpu
is about to enter the guest.
However, this creates a disconnect with userspace if the vcpu thread
returns there with any exception/PC flag set. In this case, the exposed
context is wrong, as userspace doesn't have access to these flags
(they aren't architectural). It also means that these flags are
preserved across a reset, which isn't expected.
To solve this problem, force an explicit synchronisation of the
exception state on vcpu exit to userspace. As an optimisation
for nVHE systems, only perform this when there is something pending.
Reported-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Reviewed-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
Reviewed-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Tested-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 5.11
[yuz: stable-5.12.y backport: add __KVM_HOST_SMCCC_FUNC___kvm_adjust_pc
macro manually and keep it consistent with mainline]
I'd rather you allocated a new number here, irrespective of what
mainline has (rational below).
Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_asm.h | 1 +
arch/arm64/kvm/arm.c | 11 +++++++++++
arch/arm64/kvm/hyp/exception.c | 4 ++--
arch/arm64/kvm/hyp/nvhe/hyp-main.c | 8 ++++++++
4 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index a8578d650bb6..d7f769bb6c9c 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -57,6 +57,7 @@
#define __KVM_HOST_SMCCC_FUNC___kvm_get_mdcr_el2 12
#define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs 13
#define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs 14
+#define __KVM_HOST_SMCCC_FUNC___kvm_adjust_pc 21
This is going to generate a larger than necessary host_hcall array in
hyp/nvhe/hyp-main.c, which we're trying to keep tightly packed for
obvious reasons.
It isn't obvious to me ;-). But this creates some invalid entries
(HVC handlers) in the host_hcall array, which is not good. I'll change
__KVM_HOST_SMCCC_FUNC___kvm_adjust_pc to 15. Thanks for your reminder.
With this nit fixed:
Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
Thanks!
Zenghui
