Re: [PATCH v3 15/15] Drivers: hv: Add modules to expose /dev/mshv to VMMs running on Hyper-V

From: Greg KH <gregkh@linuxfoundation.org>
To: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Cc: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
	x86@kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-arch@vger.kernel.org, patches@lists.linux.dev,
	mikelley@microsoft.com, kys@microsoft.com, wei.liu@kernel.org,
	haiyangz@microsoft.com, decui@microsoft.com,
	apais@linux.microsoft.com, Tianyu.Lan@microsoft.com,
	ssengar@linux.microsoft.com, mukeshrathor@microsoft.com,
	stanislav.kinsburskiy@gmail.com, jinankjain@linux.microsoft.com,
	vkuznets@redhat.com, tglx@linutronix.de, mingo@redhat.com,
	bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com,
	will@kernel.org, catalin.marinas@arm.com
Subject: Re: [PATCH v3 15/15] Drivers: hv: Add modules to expose /dev/mshv to VMMs running on Hyper-V
Date: Sat, 23 Sep 2023 09:58:45 +0200	[thread overview]
Message-ID: <2023092342-staunch-chafe-1598@gregkh> (raw)
In-Reply-To: <1695407915-12216-16-git-send-email-nunodasneves@linux.microsoft.com>

On Fri, Sep 22, 2023 at 11:38:35AM -0700, Nuno Das Neves wrote:
> +static int mshv_vtl_get_vsm_regs(void)
> +{
> +	struct hv_register_assoc registers[2];
> +	union hv_input_vtl input_vtl;
> +	int ret, count = 2;
> +
> +	input_vtl.as_uint8 = 0;
> +	registers[0].name = HV_REGISTER_VSM_CODE_PAGE_OFFSETS;
> +	registers[1].name = HV_REGISTER_VSM_CAPABILITIES;
> +
> +	ret = hv_call_get_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
> +				       count, input_vtl, registers);
> +	if (ret)
> +		return ret;
> +
> +	mshv_vsm_page_offsets.as_uint64 = registers[0].value.reg64;
> +	mshv_vsm_capabilities.as_uint64 = registers[1].value.reg64;
> +
> +	pr_debug("%s: VSM code page offsets: %#016llx\n", __func__,
> +		 mshv_vsm_page_offsets.as_uint64);
> +	pr_info("%s: VSM capabilities: %#016llx\n", __func__,
> +		mshv_vsm_capabilities.as_uint64);

When drivers are working properly, they are quiet.  This is very noisy
and probably is leaking memory addresses to userspace?

Also, there is NEVER a need for __func__ in a pr_debug() line, it has
that for you automatically.

Also, drivers should never call pr_*() calls, always use the proper
dev_*() calls instead.

> +
> +	return ret;
> +}
> +
> +static int mshv_vtl_configure_vsm_partition(void)
> +{
> +	union hv_register_vsm_partition_config config;
> +	struct hv_register_assoc reg_assoc;
> +	union hv_input_vtl input_vtl;
> +
> +	config.as_u64 = 0;
> +	config.default_vtl_protection_mask = HV_MAP_GPA_PERMISSIONS_MASK;
> +	config.enable_vtl_protection = 1;
> +	config.zero_memory_on_reset = 1;
> +	config.intercept_vp_startup = 1;
> +	config.intercept_cpuid_unimplemented = 1;
> +
> +	if (mshv_vsm_capabilities.intercept_page_available) {
> +		pr_debug("%s: using intercept page", __func__);

Again, __func__ is not needed, you are providing it twice here for no
real reason except to waste storage space :)

> +		config.intercept_page = 1;
> +	}
> +
> +	reg_assoc.name = HV_REGISTER_VSM_PARTITION_CONFIG;
> +	reg_assoc.value.reg64 = config.as_u64;
> +	input_vtl.as_uint8 = 0;
> +
> +	return hv_call_set_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
> +				       1, input_vtl, &reg_assoc);

None of this needs to be unwound if initialization fails later on?

thanks,

greg k-h