linux-kernel - Re: [PATCH v9 23/27] virt: gunyah: Add IO handlers

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Message-ID: <20230206104637.GG332@quicinc.com>
Date:   Mon, 6 Feb 2023 16:16:37 +0530
From:   Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>
To:     Elliot Berman <quic_eberman@...cinc.com>
CC:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Alex Elder <elder@...aro.org>,
        Murali Nalajala <quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Carl van Schaik <quic_cvanscha@...cinc.com>,
        Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...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>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Sudeep Holla <sudeep.holla@....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 v9 23/27] virt: gunyah: Add IO handlers

* Elliot Berman <quic_eberman@...cinc.com> [2023-01-20 14:46:22]:

> +static inline bool gh_vm_io_handler_matches(struct gunyah_vm_io_handler *io_hdlr, u64 addr,
> +						u64 len, u64 data)
> +{
> +	u64 mask = BIT_ULL(io_hdlr->len * BITS_PER_BYTE) - 1;
> +
> +	if (io_hdlr->addr != addr)

Isn't this test redundant (given that caller would have performed same test)?

> +		return false;
> +
> +	if (!io_hdlr->datamatch)
> +		return true;
> +
> +	if (io_hdlr->len != len)
> +		return false;
> +
> +	return (data & mask) == (io_hdlr->data & mask);
> +}
> +
> +static struct gunyah_vm_io_handler *gh_vm_mgr_find_io_hdlr(struct gunyah_vm *ghvm, u64 addr,
> +								u64 len, u64 data)
> +{
> +	struct gunyah_vm_io_handler *io_hdlr = NULL;
> +	struct rb_node *root = NULL;
> +
> +	root = ghvm->mmio_handler_root.rb_node;
> +	while (root) {
> +		io_hdlr = rb_entry(root, struct gunyah_vm_io_handler, node);
> +		if (addr < io_hdlr->addr)
> +			root = root->rb_left;
> +		else if (addr > io_hdlr->addr)
> +			root = root->rb_right;
> +		else if (gh_vm_io_handler_matches(io_hdlr, addr, len, data))

In case of handler not matching, don't we need to modify root?
Otherwise we can be stuck in infinite loop here AFAICS.

> +			return io_hdlr;
> +	}
> +	return NULL;
> +}

// snip

> +int gh_vm_mgr_add_io_handler(struct gunyah_vm *ghvm, struct gunyah_vm_io_handler *io_hdlr)
> +{
> +	struct rb_node **root, *parent = NULL;
> +
> +	if (io_hdlr->datamatch &&
> +		(!io_hdlr->len || io_hdlr->len > (sizeof(io_hdlr->data) * BITS_PER_BYTE)))
> +		return -EINVAL;
> +
> +	root = &ghvm->mmio_handler_root.rb_node;
> +	while (*root) {
> +		struct gunyah_vm_io_handler *curr = rb_entry(*root, struct gunyah_vm_io_handler,
> +								node);
> +
> +		parent = *root;
> +		if (io_hdlr->addr < curr->addr)
> +			root = &((*root)->rb_left);
> +		else if (io_hdlr->addr > curr->addr)
> +			root = &((*root)->rb_right);
> +		else

We should allow two io_handlers on the same addr, but with different data
matches I think.

> +			return -EEXIST;
> +	}
> +
> +	rb_link_node(&io_hdlr->node, parent, root);
> +	rb_insert_color(&io_hdlr->node, &ghvm->mmio_handler_root);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(gh_vm_mgr_add_io_handler);