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Subject: Re: [PATCH v7 2/2] PCI: dwc: Fix MSI page leakage in suspend/resume
To:     Jisheng Zhang <Jisheng.Zhang@synaptics.com>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Rob Herring <robh@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Jingoo Han <jingoohan1@gmail.com>,
        Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Cc:     linux-pci@vger.kernel.org, linux-omap@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
References: <20201009155311.22d3caa5@xhacker.debian>
 <20201009155505.5a580ef5@xhacker.debian>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <38a00dde-598f-b6de-ecf3-5d012bd7594a@arm.com>
Date:   Mon, 12 Oct 2020 12:37:34 +0100
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On 2020-10-09 08:55, Jisheng Zhang wrote:
> Currently, dw_pcie_msi_init() allocates and maps page for msi, then
> program the PCIE_MSI_ADDR_LO and PCIE_MSI_ADDR_HI. The Root Complex
> may lose power during suspend-to-RAM, so when we resume, we want to
> redo the latter but not the former. If designware based driver (for
> example, pcie-tegra194.c) calls dw_pcie_msi_init() in resume path, the
> msi page will be leaked.
> 
> As pointed out by Rob and Ard, there's no need to allocate a page for
> the MSI address, we could use an address in the driver data.
> 
> To avoid map the MSI msg again during resume, we move the map MSI msg
> from dw_pcie_msi_init() to dw_pcie_host_init().

You should move the unmap there as well. As soon as you know what the 
relevant address would be if you *were* to do DMA to this location, then 
the exercise is complete. Leaving it mapped for the lifetime of the 
device in order to do not-DMA to it seems questionable (and represents 
technically incorrect API usage without at least a sync_for_cpu call 
before any other access to the data).

Another point of note is that using streaming DMA mappings at all is a 
bit fragile (regardless of this change). If the host controller itself 
has a limited DMA mask relative to physical memory (which integrators 
still seem to keep doing...) then you could end up punching your MSI 
hole right in the middle of the SWIOTLB bounce buffer, where it's then 
almost *guaranteed* to interfere with real DMA :(

If no DWC users have that problem and the current code is working well 
enough, then I see little reason not to make this partucular change to 
tidy up the implementation, just bear in mind that there's always the 
possibility of having to come back and change it yet again in future to 
make it more robust. I had it in mind that this trick was done with a 
coherent DMA allocation, which would be safe from addressing problems 
but would need to be kept around for the lifetime of the device, but 
maybe that was a different driver :/

Robin.

> Suggested-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
> Reviewed-by: Rob Herring <robh@kernel.org>
> ---
>   drivers/pci/controller/dwc/pci-dra7xx.c       | 18 +++++++++-
>   .../pci/controller/dwc/pcie-designware-host.c | 33 ++++++++++---------
>   drivers/pci/controller/dwc/pcie-designware.h  |  2 +-
>   3 files changed, 36 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-dra7xx.c b/drivers/pci/controller/dwc/pci-dra7xx.c
> index 8f0b6d644e4b..6d012d2b1e90 100644
> --- a/drivers/pci/controller/dwc/pci-dra7xx.c
> +++ b/drivers/pci/controller/dwc/pci-dra7xx.c
> @@ -466,7 +466,9 @@ static struct irq_chip dra7xx_pci_msi_bottom_irq_chip = {
>   static int dra7xx_pcie_msi_host_init(struct pcie_port *pp)
>   {
>   	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +	struct device *dev = pci->dev;
>   	u32 ctrl, num_ctrls;
> +	int ret;
>   
>   	pp->msi_irq_chip = &dra7xx_pci_msi_bottom_irq_chip;
>   
> @@ -482,7 +484,21 @@ static int dra7xx_pcie_msi_host_init(struct pcie_port *pp)
>   				    ~0);
>   	}
>   
> -	return dw_pcie_allocate_domains(pp);
> +	ret = dw_pcie_allocate_domains(pp);
> +	if (ret)
> +		return ret;
> +
> +	pp->msi_data = dma_map_single_attrs(dev, &pp->msi_msg,
> +					   sizeof(pp->msi_msg),
> +					   DMA_FROM_DEVICE,
> +					   DMA_ATTR_SKIP_CPU_SYNC);
> +	ret = dma_mapping_error(dev, pp->msi_data);
> +	if (ret) {
> +		dev_err(dev, "Failed to map MSI data\n");
> +		pp->msi_data = 0;
> +		dw_pcie_free_msi(pp);
> +	}
> +	return ret;
>   }
>   
>   static const struct dw_pcie_host_ops dra7xx_pcie_host_ops = {
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index d3e9ea11ce9e..d02c7e74738d 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -266,30 +266,23 @@ void dw_pcie_free_msi(struct pcie_port *pp)
>   	irq_domain_remove(pp->msi_domain);
>   	irq_domain_remove(pp->irq_domain);
>   
> -	if (pp->msi_page)
> -		__free_page(pp->msi_page);
> +	if (pp->msi_data) {
> +		struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +		struct device *dev = pci->dev;
> +
> +		dma_unmap_single_attrs(dev, pp->msi_data, sizeof(pp->msi_msg),
> +				       DMA_FROM_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
> +	}
>   }
>   
>   void dw_pcie_msi_init(struct pcie_port *pp)
>   {
>   	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> -	struct device *dev = pci->dev;
> -	u64 msi_target;
> +	u64 msi_target = (u64)pp->msi_data;
>   
>   	if (!IS_ENABLED(CONFIG_PCI_MSI))
>   		return;
>   
> -	pp->msi_page = alloc_page(GFP_KERNEL);
> -	pp->msi_data = dma_map_page(dev, pp->msi_page, 0, PAGE_SIZE,
> -				    DMA_FROM_DEVICE);
> -	if (dma_mapping_error(dev, pp->msi_data)) {
> -		dev_err(dev, "Failed to map MSI data\n");
> -		__free_page(pp->msi_page);
> -		pp->msi_page = NULL;
> -		return;
> -	}
> -	msi_target = (u64)pp->msi_data;
> -
>   	/* Program the msi_data */
>   	dw_pcie_writel_dbi(pci, PCIE_MSI_ADDR_LO, lower_32_bits(msi_target));
>   	dw_pcie_writel_dbi(pci, PCIE_MSI_ADDR_HI, upper_32_bits(msi_target));
> @@ -394,6 +387,16 @@ int dw_pcie_host_init(struct pcie_port *pp)
>   				irq_set_chained_handler_and_data(pp->msi_irq,
>   							    dw_chained_msi_isr,
>   							    pp);
> +
> +			pp->msi_data = dma_map_single_attrs(pci->dev, &pp->msi_msg,
> +						      sizeof(pp->msi_msg),
> +						      DMA_FROM_DEVICE,
> +						      DMA_ATTR_SKIP_CPU_SYNC);
> +			if (dma_mapping_error(pci->dev, pp->msi_data)) {
> +				dev_err(pci->dev, "Failed to map MSI data\n");
> +				pp->msi_data = 0;
> +				goto err_free_msi;
> +			}
>   		} else {
>   			ret = pp->ops->msi_host_init(pp);
>   			if (ret < 0)
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 97c7063b9e89..9d2f511f13fa 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -190,8 +190,8 @@ struct pcie_port {
>   	int			msi_irq;
>   	struct irq_domain	*irq_domain;
>   	struct irq_domain	*msi_domain;
> +	u16			msi_msg;
>   	dma_addr_t		msi_data;
> -	struct page		*msi_page;
>   	struct irq_chip		*msi_irq_chip;
>   	u32			num_vectors;
>   	u32			irq_mask[MAX_MSI_CTRLS];
>