linux-kernel - Re: [PATCH v10 12/26] gunyah: vm_mgr: Add/remove user memory regions

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Date:   Thu, 16 Feb 2023 07:38:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Elliot Berman <quic_eberman@...cinc.com>
Cc:     Alex Elder <elder@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
        Murali Nalajala <quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>,
        Carl van Schaik <quic_cvanscha@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v10 12/26] gunyah: vm_mgr: Add/remove user memory regions

On Tue, Feb 14, 2023 at 01:24:16PM -0800, Elliot Berman wrote:
> 
> When launching a virtual machine, Gunyah userspace allocates memory for
> the guest and informs Gunyah about these memory regions through
> SET_USER_MEMORY_REGION ioctl.

It also frees memory, see below.  Why not document that?

> +	case GH_VM_SET_USER_MEM_REGION: {
> +		struct gh_userspace_memory_region region;
> +
> +		if (copy_from_user(&region, argp, sizeof(region)))
> +			return -EFAULT;
> +
> +		/* All other flag bits are reserved for future use */
> +		if (region.flags & ~(GH_MEM_ALLOW_READ | GH_MEM_ALLOW_WRITE | GH_MEM_ALLOW_EXEC |
> +			GH_MEM_LENT))
> +			return -EINVAL;

Nice, thanks for validating that.


> +
> +

Nit, 2 blank lines are not needed :(


> +		if (region.memory_size)
> +			r = gh_vm_mem_alloc(ghvm, &region);
> +		else
> +			r = gh_vm_mem_free(ghvm, region.label);

So if you set the size to 0 it is freed?  Wouldn't a separate ioctl make
more sense?  Where is this logic documented to userspace?

thanks,

greg k-h