linux-kernel - Re: [PATCH v10 13/26] gunyah: vm_mgr: Add ioctls to support basic non-proxy VM boot

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Message-ID: <20230220091544.GN332@quicinc.com>
Date:   Mon, 20 Feb 2023 14:45:44 +0530
From:   Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>
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>,
        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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 13/26] gunyah: vm_mgr: Add ioctls to support basic
 non-proxy VM boot

* Elliot Berman <quic_eberman@...cinc.com> [2023-02-14 13:24:26]:

>  static void gh_vm_free(struct work_struct *work)
>  {
>  	struct gh_vm *ghvm = container_of(work, struct gh_vm, free_work);
>  	struct gh_vm_mem *mapping, *tmp;
>  	int ret;
>  
> -	mutex_lock(&ghvm->mm_lock);
> -	list_for_each_entry_safe(mapping, tmp, &ghvm->memory_mappings, list) {
> -		gh_vm_mem_reclaim(ghvm, mapping);
> -		kfree(mapping);
> +	switch (ghvm->vm_status) {
> +unknown_state:
> +	case GH_RM_VM_STATUS_RUNNING:
> +		gh_vm_stop(ghvm);
> +		fallthrough;
> +	case GH_RM_VM_STATUS_INIT_FAILED:
> +	case GH_RM_VM_STATUS_LOAD:
> +	case GH_RM_VM_STATUS_LOAD_FAILED:
> +		mutex_lock(&ghvm->mm_lock);
> +		list_for_each_entry_safe(mapping, tmp, &ghvm->memory_mappings, list) {
> +			gh_vm_mem_reclaim(ghvm, mapping);
> +			kfree(mapping);
> +		}
> +		mutex_unlock(&ghvm->mm_lock);
> +		fallthrough;
> +	case GH_RM_VM_STATUS_NO_STATE:
> +		ret = gh_rm_dealloc_vmid(ghvm->rm, ghvm->vmid);
> +		if (ret)
> +			pr_warn("Failed to deallocate vmid: %d\n", ret);
> +
> +		gh_rm_notifier_unregister(ghvm->rm, &ghvm->nb);
> +		put_gh_rm(ghvm->rm);
> +		kfree(ghvm);
> +		break;
> +	default:
> +		pr_err("VM is unknown state: %d, assuming it's running.\n", ghvm->vm_status);
> +		goto unknown_state;

'goto unknown_state' here leads to a infinite loop AFAICS. For example consider
the case  where VM_START failed (due to mem_lend operation) causing VM state to
be GH_RM_VM_STATUS_RESET. A subsequent close(vmfd) can leads to that forever
loop.

//snip


> +static int gh_vm_start(struct gh_vm *ghvm)
> +{
> +	struct gh_vm_mem *mapping;
> +	u64 dtb_offset;
> +	u32 mem_handle;
> +	int ret;
> +
> +	down_write(&ghvm->status_lock);
> +	if (ghvm->vm_status != GH_RM_VM_STATUS_LOAD) {
> +		up_write(&ghvm->status_lock);
> +		return 0;
> +	}
> +
> +	ghvm->vm_status = GH_RM_VM_STATUS_RESET;
> +
> +	list_for_each_entry(mapping, &ghvm->memory_mappings, list) {

We don't seem to have the right lock here while walking the list.