Re: [PATCH v2 1/6] arm64/hyperv: Support DeviceTree

From: Elliot Berman <quic_eberman@quicinc.com>
To: Roman Kisel <romank@linux.microsoft.com>
Cc: <arnd@arndb.de>, <bhelgaas@google.com>, <bp@alien8.de>,
	<catalin.marinas@arm.com>, <dave.hansen@linux.intel.com>,
	<decui@microsoft.com>, <haiyangz@microsoft.com>, <hpa@zytor.com>,
	<kw@linux.com>, <kys@microsoft.com>, <lenb@kernel.org>,
	<lpieralisi@kernel.org>, <mingo@redhat.com>,
	<mhklinux@outlook.com>, <rafael@kernel.org>, <robh@kernel.org>,
	<tglx@linutronix.de>, <wei.liu@kernel.org>, <will@kernel.org>,
	<linux-acpi@vger.kernel.org>, <linux-arch@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-hyperv@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<linux-pci@vger.kernel.org>, <x86@kernel.org>,
	<ssengar@microsoft.com>, <sunilmut@microsoft.com>,
	<vdso@hexbites.dev>
Subject: Re: [PATCH v2 1/6] arm64/hyperv: Support DeviceTree
Date: Wed, 15 May 2024 15:02:54 -0700	[thread overview]
Message-ID: <20240515143359142-0700.eberman@hu-eberman-lv.qualcomm.com> (raw)
In-Reply-To: <20240514224508.212318-2-romank@linux.microsoft.com>

On Tue, May 14, 2024 at 03:43:48PM -0700, Roman Kisel wrote:
> The Virtual Trust Level platforms rely on DeviceTree, and the
> arm64/hyperv code supports ACPI only. Update the logic to
> support DeviceTree on boot as well as ACPI.

Could you use Call UID query from SMCCC? KVM [1] and Gunyah [2] have
been using this to identify if guest is running under those respective
hypervisors. This works in both DT and ACPI cases.

[1]: https://lore.kernel.org/all/20210330145430.996981-2-maz@kernel.org/
[2]: https://lore.kernel.org/all/20240222-gunyah-v17-4-1e9da6763d38@quicinc.com/
> 
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> ---
>  arch/arm64/hyperv/mshyperv.c | 34 +++++++++++++++++++++++++++++-----
>  1 file changed, 29 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> index b1a4de4eee29..208a3bcb9686 100644
> --- a/arch/arm64/hyperv/mshyperv.c
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -15,6 +15,9 @@
>  #include <linux/errno.h>
>  #include <linux/version.h>
>  #include <linux/cpuhotplug.h>
> +#include <linux/libfdt.h>
> +#include <linux/of.h>
> +#include <linux/of_fdt.h>
>  #include <asm/mshyperv.h>
>  
>  static bool hyperv_initialized;
> @@ -27,6 +30,29 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
>  	return 0;
>  }
>  
> +static bool hyperv_detect_fdt(void)
> +{
> +#ifdef CONFIG_OF
> +	const unsigned long hyp_node = of_get_flat_dt_subnode_by_name(
> +			of_get_flat_dt_root(), "hypervisor");
> +
> +	return (hyp_node != -FDT_ERR_NOTFOUND) &&
> +			of_flat_dt_is_compatible(hyp_node, "microsoft,hyperv");
> +#else
> +	return false;
> +#endif
> +}
> +
> +static bool hyperv_detect_acpi(void)
> +{
> +#ifdef CONFIG_ACPI
> +	return !acpi_disabled &&
> +			!strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8);
> +#else
> +	return false;
> +#endif
> +}
> +
>  static int __init hyperv_init(void)
>  {
>  	struct hv_get_vp_registers_output	result;
> @@ -35,13 +61,11 @@ static int __init hyperv_init(void)
>  
>  	/*
>  	 * Allow for a kernel built with CONFIG_HYPERV to be running in
> -	 * a non-Hyper-V environment, including on DT instead of ACPI.
> +	 * a non-Hyper-V environment.
> +	 *
>  	 * In such cases, do nothing and return success.
>  	 */
> -	if (acpi_disabled)
> -		return 0;
> -
> -	if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
> +	if (!hyperv_detect_fdt() && !hyperv_detect_acpi())
>  		return 0;
>  
>  	/* Setup the guest ID */
> -- 
> 2.45.0
> 
> 
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