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

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Message-ID: <94992117-2cab-71e6-f38c-bded109171d2@quicinc.com>
Date:   Thu, 16 Feb 2023 09:24:45 -0800
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 2/15/2023 10:38 PM, Greg Kroah-Hartman wrote:
> 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?
> 

I can mention in commit text, too.

>> +	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? >

We're following KVM convention here. The logic is documented in patch 17/26.

Thanks,
Elliot