Re: [PATCH v5 17/40] KVM: arm64: Move userspace system registers into separate function

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Hi Christoffer,

On 27/02/18 11:34, Christoffer Dall wrote:

From: Christoffer Dall <christoffer.dall@xxxxxxxxxx>

There's a semantic difference between the EL1 registers that control
operation of a kernel running in EL1 and EL1 registers that only control
userspace execution in EL0.  Since we can defer saving/restoring the
latter, move them into their own function.

The ARMv8 ARM (ARM DDI 0487C.a) Section D10.2.1 recommends that
ACTLR_EL1 has no effect on the processor when running the VHE host, and
we can therefore move this register into the EL1 state which is only
saved/restored on vcpu_put/load for a VHE host.

We also take this chance to rename the function saving/restoring the
remaining system register to make it clear this function deals with
the EL1 system registers.

Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>


Reviewed-by: Julien Grall <julien.grall@xxxxxxx>

Cheers,


---

Notes:
     Changes since v4:
      - Clarified rationale for deferring ACTLR_EL1 in the commit message.
Changes since v3: 
      - Correct the comment about ACTLR_EL1 and adjust commit text.
Changes since v2: 
      - Save restore ACTLR_EL1 as part of the EL1 registers state instead of
        the user register state, as ACTLR_EL1 can't affect the host's execution
        on VHE systems.
Changes since v1: 
      - Added comment about sp_el0 to common save sysreg save/restore functions

  arch/arm64/kvm/hyp/sysreg-sr.c | 48 ++++++++++++++++++++++++++++++------------
  1 file changed, 35 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index 99fc60516103..d5a5145b4e7c 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c
@@ -28,24 +28,33 @@ static void __hyp_text __sysreg_do_nothing(struct kvm_cpu_context *ctxt) { }
  /*
   * Non-VHE: Both host and guest must save everything.
   *
- * VHE: Host must save tpidr*_el0, actlr_el1, mdscr_el1, sp_el0,
+ * VHE: Host must save tpidr*_el0, mdscr_el1, sp_el0,
   * and guest must save everything.
   */
static void __hyp_text __sysreg_save_common_state(struct kvm_cpu_context *ctxt) 
  {
-	ctxt->sys_regs[ACTLR_EL1]	= read_sysreg(actlr_el1);
-	ctxt->sys_regs[TPIDR_EL0]	= read_sysreg(tpidr_el0);
-	ctxt->sys_regs[TPIDRRO_EL0]	= read_sysreg(tpidrro_el0);
  	ctxt->sys_regs[MDSCR_EL1]	= read_sysreg(mdscr_el1);
+
+	/*
+	 * The host arm64 Linux uses sp_el0 to point to 'current' and it must
+	 * therefore be saved/restored on every entry/exit to/from the guest.
+	 */
  	ctxt->gp_regs.regs.sp		= read_sysreg(sp_el0);
  }
-static void __hyp_text __sysreg_save_state(struct kvm_cpu_context *ctxt) 
+static void __hyp_text __sysreg_save_user_state(struct kvm_cpu_context *ctxt)
+{
+	ctxt->sys_regs[TPIDR_EL0]	= read_sysreg(tpidr_el0);
+	ctxt->sys_regs[TPIDRRO_EL0]	= read_sysreg(tpidrro_el0);
+}
+
+static void __hyp_text __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
  {
  	ctxt->sys_regs[MPIDR_EL1]	= read_sysreg(vmpidr_el2);
  	ctxt->sys_regs[CSSELR_EL1]	= read_sysreg(csselr_el1);
  	ctxt->sys_regs[SCTLR_EL1]	= read_sysreg_el1(sctlr);
+	ctxt->sys_regs[ACTLR_EL1]	= read_sysreg(actlr_el1);
  	ctxt->sys_regs[CPACR_EL1]	= read_sysreg_el1(cpacr);
  	ctxt->sys_regs[TTBR0_EL1]	= read_sysreg_el1(ttbr0);
  	ctxt->sys_regs[TTBR1_EL1]	= read_sysreg_el1(ttbr1);
@@ -73,35 +82,46 @@ static void __hyp_text __sysreg_save_state(struct kvm_cpu_context *ctxt)
  }
static hyp_alternate_select(__sysreg_call_save_host_state, 
-			    __sysreg_save_state, __sysreg_do_nothing,
+			    __sysreg_save_el1_state, __sysreg_do_nothing,
  			    ARM64_HAS_VIRT_HOST_EXTN);
void __hyp_text __sysreg_save_host_state(struct kvm_cpu_context *ctxt) 
  {
  	__sysreg_call_save_host_state()(ctxt);
  	__sysreg_save_common_state(ctxt);
+	__sysreg_save_user_state(ctxt);
  }
void __hyp_text __sysreg_save_guest_state(struct kvm_cpu_context *ctxt) 
  {
-	__sysreg_save_state(ctxt);
+	__sysreg_save_el1_state(ctxt);
  	__sysreg_save_common_state(ctxt);
+	__sysreg_save_user_state(ctxt);
  }
static void __hyp_text __sysreg_restore_common_state(struct kvm_cpu_context *ctxt) 
  {
-	write_sysreg(ctxt->sys_regs[ACTLR_EL1],	  actlr_el1);
-	write_sysreg(ctxt->sys_regs[TPIDR_EL0],	  tpidr_el0);
-	write_sysreg(ctxt->sys_regs[TPIDRRO_EL0], tpidrro_el0);
  	write_sysreg(ctxt->sys_regs[MDSCR_EL1],	  mdscr_el1);
+
+	/*
+	 * The host arm64 Linux uses sp_el0 to point to 'current' and it must
+	 * therefore be saved/restored on every entry/exit to/from the guest.
+	 */
  	write_sysreg(ctxt->gp_regs.regs.sp,	  sp_el0);
  }
-static void __hyp_text __sysreg_restore_state(struct kvm_cpu_context *ctxt) 
+static void __hyp_text __sysreg_restore_user_state(struct kvm_cpu_context *ctxt)
+{
+	write_sysreg(ctxt->sys_regs[TPIDR_EL0],	  	tpidr_el0);
+	write_sysreg(ctxt->sys_regs[TPIDRRO_EL0], 	tpidrro_el0);
+}
+
+static void __hyp_text __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
  {
  	write_sysreg(ctxt->sys_regs[MPIDR_EL1],		vmpidr_el2);
  	write_sysreg(ctxt->sys_regs[CSSELR_EL1],	csselr_el1);
  	write_sysreg_el1(ctxt->sys_regs[SCTLR_EL1],	sctlr);
+	write_sysreg(ctxt->sys_regs[ACTLR_EL1],	  	actlr_el1);
  	write_sysreg_el1(ctxt->sys_regs[CPACR_EL1],	cpacr);
  	write_sysreg_el1(ctxt->sys_regs[TTBR0_EL1],	ttbr0);
  	write_sysreg_el1(ctxt->sys_regs[TTBR1_EL1],	ttbr1);
@@ -129,19 +149,21 @@ static void __hyp_text __sysreg_restore_state(struct kvm_cpu_context *ctxt)
  }
static hyp_alternate_select(__sysreg_call_restore_host_state, 
-			    __sysreg_restore_state, __sysreg_do_nothing,
+			    __sysreg_restore_el1_state, __sysreg_do_nothing,
  			    ARM64_HAS_VIRT_HOST_EXTN);
void __hyp_text __sysreg_restore_host_state(struct kvm_cpu_context *ctxt) 
  {
  	__sysreg_call_restore_host_state()(ctxt);
  	__sysreg_restore_common_state(ctxt);
+	__sysreg_restore_user_state(ctxt);
  }
void __hyp_text __sysreg_restore_guest_state(struct kvm_cpu_context *ctxt) 
  {
-	__sysreg_restore_state(ctxt);
+	__sysreg_restore_el1_state(ctxt);
  	__sysreg_restore_common_state(ctxt);
+	__sysreg_restore_user_state(ctxt);
  }
void __hyp_text __sysreg32_save_state(struct kvm_vcpu *vcpu) 



--
Julien Grall
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