Re: [PATCH v2 20/21] arm64: VHE: Add support for running Linux in EL2 mode

From: Christoffer Dall
Date: Mon Feb 01 2016 - 10:25:53 EST


On Mon, Jan 25, 2016 at 03:53:54PM +0000, Marc Zyngier wrote:
> With ARMv8.1 VHE, the architecture is able to (almost) transparently
> run the kernel at EL2, despite being written for EL1.
>
> This patch takes care of the "almost" part, mostly preventing the kernel
> from dropping from EL2 to EL1, and setting up the HYP configuration.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
> arch/arm64/Kconfig | 13 +++++++++++++
> arch/arm64/kernel/head.S | 32 +++++++++++++++++++++++++++++++-
> 2 files changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 8cc6228..ada34df 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -750,6 +750,19 @@ config ARM64_LSE_ATOMICS
> not support these instructions and requires the kernel to be
> built with binutils >= 2.25.
>
> +config ARM64_VHE
> + bool "Enable support for Virtualization Host Extension (VHE)"

Extensions (plural)

> + default y
> + help
> + Virtualization Host Extension (VHE) allows the kernel to run

same

> + directly at EL2 (instead of EL1) on processors that support
> + it. This leads to better performance for KVM, as it reduces

s/it/them/ then?

> + the cost of the world switch.
> +
> + Selecting this option allows the VHE feature to be detected
> + at runtime, and does not affect processors that do not
> + implement this feature.
> +
> endmenu
>
> endmenu
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index ffe9c2b..2a7134c 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -30,6 +30,7 @@
> #include <asm/cache.h>
> #include <asm/cputype.h>
> #include <asm/kernel-pgtable.h>
> +#include <asm/kvm_mmu.h>
> #include <asm/memory.h>
> #include <asm/pgtable-hwdef.h>
> #include <asm/pgtable.h>
> @@ -464,8 +465,25 @@ CPU_LE( bic x0, x0, #(3 << 24) ) // Clear the EE and E0E bits for EL1
> isb
> ret
>
> +2:
> +#ifdef CONFIG_ARM64_VHE
> + /*
> + * Check for VHE being present. For the rest of the EL2 setup,
> + * x2 being non-zero indicates that we do have VHE, and that the
> + * kernel is intended to run at EL2.
> + */
> + mrs x2, id_aa64mmfr1_el1
> + ubfx x2, x2, #8, #4
> +#else
> + mov x2, xzr
> +#endif
> +
> /* Hyp configuration. */
> -2: mov x0, #(1 << 31) // 64-bit EL1
> + mov x0, #HCR_RW // 64-bit EL1
> + cbz x2, set_hcr
> + orr x0, x0, #HCR_TGE // Enable Host Extensions
> + orr x0, x0, #HCR_E2H
> +set_hcr:
> msr hcr_el2, x0
>
> /* Generic timers. */
> @@ -507,6 +525,9 @@ CPU_LE( movk x0, #0x30d0, lsl #16 ) // Clear EE and E0E on LE systems
>
> /* Coprocessor traps. */
> mov x0, #0x33ff
> + cbz x2, set_cptr
> + orr x0, x0, #(3 << 20) // Don't trap FP

nit: If you make that define we discussed earlier you can use it here too

> +set_cptr:
> msr cptr_el2, x0 // Disable copro. traps to EL2
>
> #ifdef CONFIG_COMPAT
> @@ -521,6 +542,15 @@ CPU_LE( movk x0, #0x30d0, lsl #16 ) // Clear EE and E0E on LE systems
> /* Stage-2 translation */
> msr vttbr_el2, xzr
>
> + cbz x2, install_el2_stub
> +
> + setup_vtcr x4, x5
> +
> + mov w20, #BOOT_CPU_MODE_EL2 // This CPU booted in EL2
> + isb
> + ret
> +
> +install_el2_stub:
> /* Hypervisor stub */
> adrp x0, __hyp_stub_vectors
> add x0, x0, #:lo12:__hyp_stub_vectors
> --
> 2.1.4
>

Otherwise:

Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>