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Subject: Re: [RFC PATCH v4 1/7] PCI: Add a new option for resource_alignment
 to reassign alignment
To: Yongji Xie <xyjxie@linux.vnet.ibm.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org
References: <1457336918-3893-1-git-send-email-xyjxie@linux.vnet.ibm.com>
 <1457336918-3893-2-git-send-email-xyjxie@linux.vnet.ibm.com>
Cc: bhelgaas@google.com, corbet@lwn.net, alex.williamson@redhat.com,
        benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
        warrier@linux.vnet.ibm.com, zhong@linux.vnet.ibm.com,
        nikunj@linux.vnet.ibm.com
From: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-ID: <56E0D9BB.5010300@ozlabs.ru>
Date: Thu, 10 Mar 2016 13:19:39 +1100
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On 03/07/2016 06:48 PM, Yongji Xie wrote:
> When using resource_alignment kernel parameter, the current
> implement reassigns the alignment by changing resources' size
> which can potentially break some drivers.

How can this possibly break any driver?... It rounds up, not down, what do 
I miss here?

>
> So this patch adds a new option "noresize" for the parameter
> to solve this problem.
>
> Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com>
> ---
>   Documentation/kernel-parameters.txt |    5 ++++-
>   drivers/pci/pci.c                   |   36 +++++++++++++++++++++++++----------
>   2 files changed, 30 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 9a53c92..d8b29ab 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2912,13 +2912,16 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>   				window. The default value is 64 megabytes.
>   		resource_alignment=
>   				Format:
> -				[<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
> +				[<order of align>@][<domain>:]<bus>:<slot>.<func>
> +				[:noresize][; ...]
>   				Specifies alignment and device to reassign
>   				aligned memory resources.
>   				If <order of align> is not specified,
>   				PAGE_SIZE is used as alignment.
>   				PCI-PCI bridge can be specified, if resource
>   				windows need to be expanded.
> +				noresize: Don't change the resources' sizes when
> +				reassigning alignment.
>   		ecrc=		Enable/disable PCIe ECRC (transaction layer
>   				end-to-end CRC checking).
>   				bios: Use BIOS/firmware settings. This is the
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 602eb42..760cce5 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4598,7 +4598,8 @@ static DEFINE_SPINLOCK(resource_alignment_lock);
>    * RETURNS: Resource alignment if it is specified.
>    *          Zero if it is not specified.
>    */
> -static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev)
> +static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
> +		bool *resize)
>   {
>   	int seg, bus, slot, func, align_order, count;
>   	resource_size_t align = 0;
> @@ -4626,6 +4627,11 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev)
>   			}
>   		}
>   		p += count;
> +		if (!strncmp(p, ":noresize", 9)) {
> +			*resize = false;
> +			p += 9;
> +		} else
> +			*resize = true;
>   		if (seg == pci_domain_nr(dev->bus) &&
>   			bus == dev->bus->number &&
>   			slot == PCI_SLOT(dev->devfn) &&
> @@ -4658,11 +4664,12 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
>   {
>   	int i;
>   	struct resource *r;
> +	bool resize;
>   	resource_size_t align, size;
>   	u16 command;
>
>   	/* check if specified PCI is target device to reassign */
> -	align = pci_specified_resource_alignment(dev);
> +	align = pci_specified_resource_alignment(dev, &resize);

A compiler should have warned here about passing a pointer to unitialized 
@resize.


>   	if (!align)
>   		return;
>
> @@ -4684,15 +4691,24 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
>   		if (!(r->flags & IORESOURCE_MEM))
>   			continue;
>   		size = resource_size(r);
> -		if (size < align) {
> -			size = align;
> -			dev_info(&dev->dev,
> -				"Rounding up size of resource #%d to %#llx.\n",
> -				i, (unsigned long long)size);
> +		if (resize) {
> +			if (size < align) {
> +				size = align;
> +				dev_info(&dev->dev,
> +					"Rounding up size of resource #%d to %#llx.\n",
> +					i, (unsigned long long)size);
> +			}
> +			r->flags |= IORESOURCE_UNSET;
> +			r->end = size - 1;
> +			r->start = 0;
> +		} else {
> +			if (size > align)
> +				align = size;
> +			r->flags &= ~IORESOURCE_SIZEALIGN;
> +			r->flags |= IORESOURCE_STARTALIGN | IORESOURCE_UNSET;
> +			r->start = align;
> +			r->end = r->start + size - 1;
>   		}
> -		r->flags |= IORESOURCE_UNSET;
> -		r->end = size - 1;
> -		r->start = 0;
>   	}
>   	/* Need to disable bridge's resource window,
>   	 * to enable the kernel to reassign new resource
>


-- 
Alexey