On 1/27/20 7:51 AM, Greg Kroah-Hartman wrote:

On Sun, Jan 26, 2020 at 08:52:33AM -0500, Sasha Levin wrote:

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On Sat, Jan 25, 2020 at 08:03:25PM -0800, Florian Fainelli wrote:

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Hi Greg, Sasha,

Could you backport upstream commit de19055564c8f8f9d366f8db3395836da0b2176c ("Documentation: Document arm64 kpti control") to the stable 4.9, 4.14 and 4.19 kernels since they all support the command line parameter.

Hey Florian,

We don't normally take documentation patches into stable trees.

Normally we do not, but this is simple enough I've queued it up for 4.19 and 4.14. Are you sure it is ok for 4.9? If so, Florian, can you provide a backported version of it?

Yes, I am positive this parameter is relevant for the stable-4.9 tree, too:

git show linux-stable/linux-4.9.y

static int __init parse_kpti(char *str) { bool enabled; int ret = strtobool(str, &enabled);

if (ret) return ret;

__kpti_forced = enabled ? 1 : -1; return 0; } early_param("kpti", parse_kpti);

I will be sending you a targeted patch in a short while.

On 1/29/2020 11:16 AM, Sasha Levin wrote:

On Mon, Jan 27, 2020 at 04:51:06PM +0100, Greg Kroah-Hartman wrote:

...

On Sun, Jan 26, 2020 at 08:52:33AM -0500, Sasha Levin wrote:

...

On Sat, Jan 25, 2020 at 08:03:25PM -0800, Florian Fainelli wrote:

...

Hi Greg, Sasha,

Could you backport upstream commit de19055564c8f8f9d366f8db3395836da0b2176c ("Documentation: Document

arm64

...

kpti control") to the stable 4.9, 4.14 and 4.19 kernels since they all support the command line parameter.

Hey Florian,

We don't normally take documentation patches into stable trees.

Normally we do not, but this is simple enough I've queued it up for 4.19 and 4.14.  Are you sure it is ok for 4.9?  If so, Florian, can you provide a backported version of it?

My objection to taking documentation patches is either that we take all of them, or we take none. If we take only select documentation fixes it makes a frankenstein Documentation/ directory that might cause more harm than benefit.

Let's say I'm looking for netfilter documentation on 4.19, can I trust linux-4.19.y or do I look upstream? Right now I know I have to look upstream, but if we tell people it's okay to trust the linux-4.19.y docs then we might be causing harm to our users when some fixes were backported but corresponding documentation fixes weren't.

For a high profile feature/parameter such as kpti it seems to me that making sure that the documentation reflects what the code supports is a good way to limit the amount of support requests. For other options, I would agree with you that back porting them probably makes little sense.