Re: [PATCH 3/4] KVM: arm64: Parse reserved-memory node for pkvm guest firmware region

[Mark Rutland <mark.rutland@arm.com>]

On Thu, Jun 03, 2021 at 07:33:46PM +0100, Will Deacon wrote:
> Add support for a "linux,pkvm-guest-firmware-memory" reserved memory
> region, which can be used to identify a firmware image for protected
> VMs.

The idea that the guest's FW comes from the host's FW strikes me as
unusual; what's the rationale for this coming from the host FW? IIUC
other confidential compute VM environments allow you to load up whatever
virtual FW you want, but this is measured such that the virtual FW used
can be attested.

Thanks,
Mark.

> 
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  arch/arm64/kvm/Makefile |  2 +-
>  arch/arm64/kvm/pkvm.c   | 52 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 53 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/kvm/pkvm.c
> 
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index 589921392cb1..61e054411831 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -14,7 +14,7 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \
>  	 $(KVM)/vfio.o $(KVM)/irqchip.o \
>  	 arm.o mmu.o mmio.o psci.o perf.o hypercalls.o pvtime.o \
>  	 inject_fault.o va_layout.o handle_exit.o \
> -	 guest.o debug.o reset.o sys_regs.o \
> +	 guest.o debug.o pkvm.o reset.o sys_regs.o \
>  	 vgic-sys-reg-v3.o fpsimd.o pmu.o \
>  	 arch_timer.o trng.o\
>  	 vgic/vgic.o vgic/vgic-init.o \
> diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
> new file mode 100644
> index 000000000000..7af5d03a3941
> --- /dev/null
> +++ b/arch/arm64/kvm/pkvm.c
> @@ -0,0 +1,52 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * KVM host (EL1) interface to Protected KVM (pkvm) code at EL2.
> + *
> + * Copyright (C) 2021 Google LLC
> + * Author: Will Deacon <will@kernel.org>
> + */
> +
> +#include <linux/kvm_host.h>
> +#include <linux/mm.h>
> +#include <linux/of_fdt.h>
> +#include <linux/of_reserved_mem.h>
> +
> +static struct reserved_mem *pkvm_firmware_mem;
> +
> +static int __init pkvm_firmware_rmem_err(struct reserved_mem *rmem,
> +					 const char *reason)
> +{
> +	phys_addr_t end = rmem->base + rmem->size;
> +
> +	kvm_err("Ignoring pkvm guest firmware memory reservation [%pa - %pa]: %s\n",
> +		&rmem->base, &end, reason);
> +	return -EINVAL;
> +}
> +
> +static int __init pkvm_firmware_rmem_init(struct reserved_mem *rmem)
> +{
> +	unsigned long node = rmem->fdt_node;
> +
> +	if (kvm_get_mode() != KVM_MODE_PROTECTED)
> +		return pkvm_firmware_rmem_err(rmem, "protected mode not enabled");
> +
> +	if (pkvm_firmware_mem)
> +		return pkvm_firmware_rmem_err(rmem, "duplicate reservation");
> +
> +	if (!of_get_flat_dt_prop(node, "no-map", NULL))
> +		return pkvm_firmware_rmem_err(rmem, "missing \"no-map\" property");
> +
> +	if (of_get_flat_dt_prop(node, "reusable", NULL))
> +		return pkvm_firmware_rmem_err(rmem, "\"reusable\" property unsupported");
> +
> +	if (!PAGE_ALIGNED(rmem->base))
> +		return pkvm_firmware_rmem_err(rmem, "base is not page-aligned");
> +
> +	if (!PAGE_ALIGNED(rmem->size))
> +		return pkvm_firmware_rmem_err(rmem, "size is not page-aligned");
> +
> +	pkvm_firmware_mem = rmem;
> +	return 0;
> +}
> +RESERVEDMEM_OF_DECLARE(pkvm_firmware, "linux,pkvm-guest-firmware-memory",
> +		       pkvm_firmware_rmem_init);
> -- 
> 2.32.0.rc0.204.g9fa02ecfa5-goog
>