"arm64: alternatives: use tpidr_el2 on VHE hosts" v4.9 backport missing edits to proc.S

"arm64: alternatives: use tpidr_el2 on VHE hosts" v4.9 backport missing edits to proc.S

[Stephen Warren]

James,

I'm looking at commit 6d99b68933fbcf51f84fcbba49246ce1209ec193 ("arm64: 
alternatives: use tpidr_el2 on VHE hosts"). When it was back-ported to 
v4.9.x as eea59020a7f2993018ccde317387031c04c62036, the changes to 
arch/arm64/mm/proc.S weren't included. I assume this was just an 
accident, or was there some specific reason for this? Either way, I do 
find that I need those changes for system suspend/resume to work in my 
downstream vendor fork of v4.9 if I enable KVM support in .config. I'm 
happy to send a patch for v4.9.x to add those changes back if that's the 
way to go. v4.14.x and later don't have this issue.

Thanks.

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Re: "arm64: alternatives: use tpidr_el2 on VHE hosts" v4.9 backport missing edits to proc.S

[Stephen Warren]

On 1/7/20 6:09 PM, Stephen Warren wrote:
> James,
> 
> I'm looking at commit 6d99b68933fbcf51f84fcbba49246ce1209ec193 ("arm64: 
> alternatives: use tpidr_el2 on VHE hosts"). When it was back-ported to 
> v4.9.x as eea59020a7f2993018ccde317387031c04c62036, the changes to 
> arch/arm64/mm/proc.S weren't included. I assume this was just an 
> accident, or was there some specific reason for this? Either way, I do 
> find that I need those changes for system suspend/resume to work in my 
> downstream vendor fork of v4.9 if I enable KVM support in .config. I'm 
> happy to send a patch for v4.9.x to add those changes back if that's the 
> way to go. v4.14.x and later don't have this issue.

Upon further investigation of git history, here's what happened:

When When 6d99b68933fb was back-ported to upstream v4.9.x as 
eea59020a7f2, proc.S didn't save/restore tpidr_el1 at all, so that's why 
the edits to proc.S were dropped as part of the backport.

Separately, in android-4.9, 0ec37136b90e ("UPSTREAM: arm64: move sp_el0 
and tpidr_el1 into cpu_suspend_ctx") modified proc.S to save/restore 
tpidir_el1. When those two commits were later merged together in 
android-4.9, the modifications to proc.S to alternate between 
tpidr_el1/2 should have been added back in, but weren't.

Since our downstream 4.9 fork is based on android-4.9 after that merge, 
it picked up this issue and needs to be patched for it. Anyone else 
using android-4.9 would need this fix too. However, upstream 4.9.x 
stable doesn't have an issue.

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Re: "arm64: alternatives: use tpidr_el2 on VHE hosts" v4.9 backport missing edits to proc.S

[Greg Kroah-Hartman]

On Wed, Jan 08, 2020 at 11:08:20AM -0700, Stephen Warren wrote:
> On 1/7/20 6:09 PM, Stephen Warren wrote:
> > James,
> > 
> > I'm looking at commit 6d99b68933fbcf51f84fcbba49246ce1209ec193 ("arm64:
> > alternatives: use tpidr_el2 on VHE hosts"). When it was back-ported to
> > v4.9.x as eea59020a7f2993018ccde317387031c04c62036, the changes to
> > arch/arm64/mm/proc.S weren't included. I assume this was just an
> > accident, or was there some specific reason for this? Either way, I do
> > find that I need those changes for system suspend/resume to work in my
> > downstream vendor fork of v4.9 if I enable KVM support in .config. I'm
> > happy to send a patch for v4.9.x to add those changes back if that's the
> > way to go. v4.14.x and later don't have this issue.
> 
> Upon further investigation of git history, here's what happened:
> 
> When When 6d99b68933fb was back-ported to upstream v4.9.x as eea59020a7f2,
> proc.S didn't save/restore tpidr_el1 at all, so that's why the edits to
> proc.S were dropped as part of the backport.
> 
> Separately, in android-4.9, 0ec37136b90e ("UPSTREAM: arm64: move sp_el0 and
> tpidr_el1 into cpu_suspend_ctx") modified proc.S to save/restore tpidir_el1.
> When those two commits were later merged together in android-4.9, the
> modifications to proc.S to alternate between tpidr_el1/2 should have been
> added back in, but weren't.
> 
> Since our downstream 4.9 fork is based on android-4.9 after that merge, it
> picked up this issue and needs to be patched for it. Anyone else using
> android-4.9 would need this fix too. However, upstream 4.9.x stable doesn't
> have an issue.

Thanks for figuring this out.  If you could submit a 4.9 patch to AOSP
for this, that would be great, or I can do it myself if you have a
patch.

thanks,

greg k-h

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