Subject: [PATCH 12/15] arm: KVM: Simplify HYP init

From: [email-masked] (Christoffer Dall)
Date: Tue, 28 Jun 2016 23:50:37 +0200

On Tue, Jun 07, 2016 at 11:58:32AM +0100, Marc Zyngier wrote:
> Just like for arm64, we can now make the HYP setup a lot simpler,
> and we can now initialise it in one go (instead of the two
> phases we currently have).
> 
> Signed-off-by: Marc Zyngier <[email-masked]>
> ---
>  arch/arm/include/asm/kvm_host.h | 15 +++++--------
>  arch/arm/kvm/init.S             | 49 ++++++++---------------------------------
>  2 files changed, 14 insertions(+), 50 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 020f4eb..eafbfd5 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -250,18 +250,13 @@ static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
>  	 * code. The init code doesn't need to preserve these
>  	 * registers as r0-r3 are already callee saved according to
>  	 * the AAPCS.
> -	 * Note that we slightly misuse the prototype by casing the
> +	 * Note that we slightly misuse the prototype by casting the
>  	 * stack pointer to a void *.
> -	 *
> -	 * We don't have enough registers to perform the full init in
> -	 * one go.  Install the boot PGD first, and then install the
> -	 * runtime PGD, stack pointer and vectors. The PGDs are always
> -	 * passed as the third argument, in order to be passed into
> -	 * r2-r3 to the init code (yes, this is compliant with the
> -	 * PCS!).
> -	 */
>  
> -	kvm_call_hyp(NULL, 0, boot_pgd_ptr);
> +	 * The PGDs are always passed as the third argument, in order
> +	 * to be passed into r2-r3 to the init code (yes, this is
> +	 * compliant with the PCS!).
> +	 */
>  
>  	kvm_call_hyp((void*)hyp_stack_ptr, vector_ptr, pgd_ptr);
>  }
> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
> index 1f9ae17..b82a99d 100644
> --- a/arch/arm/kvm/init.S
> +++ b/arch/arm/kvm/init.S
> @@ -32,23 +32,13 @@
>   *       r2,r3 = Hypervisor pgd pointer
>   *
>   * The init scenario is:
> - * - We jump in HYP with four parameters: boot HYP pgd, runtime HYP pgd,
> - *   runtime stack, runtime vectors
> - * - Enable the MMU with the boot pgd
> - * - Jump to a target into the trampoline page (remember, this is the same
> - *   physical page!)
> - * - Now switch to the runtime pgd (same VA, and still the same physical
> - *   page!)
> + * - We jump in HYP with 3 parameters: runtime HYP pgd, runtime stack,
> + *   runtime vectors

probably just call this HYP pgd, HYP stack, and HYP vectors now

>   * - Invalidate TLBs
>   * - Set stack and vectors
> + * - Setup the page tables
> + * - Enable the MMU
>   * - Profit! (or eret, if you only care about the code).
> - *
> - * As we only have four registers available to pass parameters (and we
> - * need six), we split the init in two phases:
> - * - Phase 1: r0 = 0, r1 = 0, r2,r3 contain the boot PGD.
> - *   Provides the basic HYP init, and enable the MMU.
> - * - Phase 2: r0 = ToS, r1 = vectors, r2,r3 contain the runtime PGD.
> - *   Switches to the runtime PGD, set stack and vectors.
>   */
>  
>  	.text
> @@ -68,8 +58,11 @@ __kvm_hyp_init:
>  	W(b)	.
>  
>  __do_hyp_init:
> -	cmp	r0, #0			@ We have a SP?
> -	bne	phase2			@ Yes, second stage init
> +	@ Set stack pointer
> +	mov	sp, r0
> +
> +	@ Set HVBAR to point to the HYP vectors
> +	mcr	p15, 4, r1, c12, c0, 0	@ HVBAR
>  
>  	@ Set the HTTBR to point to the hypervisor PGD pointer passed
>  	mcrr	p15, 4, rr_lo_hi(r2, r3), c2
> @@ -114,33 +107,9 @@ __do_hyp_init:
>   THUMB(	ldr	r2, =(HSCTLR_M | HSCTLR_A | HSCTLR_TE)		)
>  	orr	r1, r1, r2
>  	orr	r0, r0, r1
> -	isb
>  	mcr	p15, 4, r0, c1, c0, 0	@ HSCR
> -
> -	@ End of init phase-1
> -	eret
> -
> -phase2:
> -	@ Set stack pointer
> -	mov	sp, r0
> -
> -	@ Set HVBAR to point to the HYP vectors
> -	mcr	p15, 4, r1, c12, c0, 0	@ HVBAR
> -
> -	@ Jump to the trampoline page
> -	ldr	r0, =TRAMPOLINE_VA
> -	adr	r1, target
> -	bfi	r0, r1, #0, #PAGE_SHIFT
> -	ret	r0
> -
> -target:	@ We're now in the trampoline code, switch page tables
> -	mcrr	p15, 4, rr_lo_hi(r2, r3), c2
>  	isb
>  
> -	@ Invalidate the old TLBs
> -	mcr	p15, 4, r0, c8, c7, 0	@ TLBIALLH
> -	dsb	ish

how are we sure there are no stale entries in the TLB beyond the idmap
region?  Did we take care of this during kernel boot?  What about
hotplug/suspend stuff?

Thanks,
-Christoffer