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

Julien Grall Mon, 05 Mar 2018 05:01:19 -0800

Hi Christoffer,

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

From: Christoffer Dall <[email protected]>


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 <[email protected]>
Reviewed-by: Marc Zyngier <[email protected]>
Signed-off-by: Christoffer Dall <[email protected]>


Reviewed-by: Julien Grall <[email protected]>

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

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