linux-kernel - Re: [PATCH] iommu/amd: Fix extended features logging

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Date:   Sun, 11 Apr 2021 08:17:02 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Alexander Monakov <amonakov@...ras.ru>
Cc:     Joerg Roedel <jroedel@...e.de>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/amd: Fix extended features logging

Dear Alexander,


Am 10.04.21 um 23:11 schrieb Alexander Monakov:
> print_iommu_info prints the EFR register and then the decoded list of
> features on a separate line:
> 
> pci 0000:00:00.2: AMD-Vi: Extended features (0x206d73ef22254ade):
>   PPR X2APIC NX GT IA GA PC GA_vAPIC
> 
> The second line is emitted via 'pr_cont', which causes it to have a
> different ('warn') loglevel compared to the previous line ('info').
> 
> Commit 9a295ff0ffc9 attempted to rectify this by removing the newline
> from the pci_info format string, but this doesn't work, as pci_info
> calls implicitly append a newline anyway.

Hmm, did I really screw that up during my testing? I am sorry about that.

I tried to wrap my head around, where the newline is implicitly 
appended, and only found the definitions below.

     include/linux/pci.h:#define pci_info(pdev, fmt, arg...) 
dev_info(&(pdev)->dev, fmt, ##arg)

     include/linux/dev_printk.h:#define dev_info(dev, fmt, ...) 
                                      \
     include/linux/dev_printk.h:     _dev_info(dev, dev_fmt(fmt), 
##__VA_ARGS__)

     include/linux/dev_printk.h:__printf(2, 3) __cold
     include/linux/dev_printk.h:void _dev_info(const struct device *dev, 
const char *fmt, ...);

     include/linux/compiler_attributes.h:#define __printf(a, b) 
          __attribute__((__format__(printf, a, b)))


> Restore the newline, and call pr_info with empty format string to set
> the loglevel for subsequent pr_cont calls. The same solution is used in
> EFI and uvesafb drivers.

Thank you for fixing this.

> Fixes: 9a295ff0ffc9 ("iommu/amd: Print extended features in one line to fix divergent log levels")
> Signed-off-by: Alexander Monakov <amonakov@...ras.ru>
> Cc: Paul Menzel <pmenzel@...gen.mpg.de>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> Cc: iommu@...ts.linux-foundation.org
> ---
>   drivers/iommu/amd/init.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 596d0c413473..a25e241eff1c 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -1929,8 +1929,11 @@ static void print_iommu_info(void)
>   		pci_info(pdev, "Found IOMMU cap 0x%hx\n", iommu->cap_ptr);
>   
>   		if (iommu->cap & (1 << IOMMU_CAP_EFR)) {
> -			pci_info(pdev, "Extended features (%#llx):",
> +			pci_info(pdev, "Extended features (%#llx):\n",
>   				 iommu->features);
> +
> +			pr_info("");
> +
>   			for (i = 0; i < ARRAY_SIZE(feat_str); ++i) {
>   				if (iommu_feature(iommu, (1ULL << i)))
>   					pr_cont(" %s", feat_str[i]);
> 

In the discussion *smpboot: CPU numbers printed as warning* [1] John wrote:

> It is supported to provide loglevels for CONT messages. The loglevel is
> then only used if the append fails:
> 
>     pr_cont(KERN_INFO "message part");
> 
> I don't know if we want to go down that path. But it is supported.


Kind regards,

Paul


[1]: https://lkml.org/lkml/2021/2/16/191