linux-kernel - Re: [PATCH v2 1/3] x86/xen: Avoid fast syscall path for Xen PV guests

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Date:	Tue, 15 Dec 2015 10:21:37 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com
Cc:	david.vrabel@...rix.com, konrad.wilk@...cle.com, luto@...nel.org,
	bp@...e.de, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 1/3] x86/xen: Avoid fast syscall path for Xen PV guests

On 11/19/2015 04:55 PM, Boris Ostrovsky wrote:
> After 32-bit syscall rewrite, and specifically after commit 5f310f739b4c
> ("x86/entry/32: Re-implement SYSENTER using the new C path"), the stack
> frame that is passed to xen_sysexit is no longer a "standard" one (i.e.
> it's not pt_regs).
>
> Since we end up calling xen_iret from xen_sysexit we don't need to fix
> up the stack and instead follow entry_SYSENTER_32's IRET path directly
> to xen_iret.
>
> We can do the same thing for compat mode even though stack does not need
> to be fixed. This will allow us to drop usergs_sysret32 paravirt op (in
> the subsequent patch)
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Suggested-by: Andy Lutomirski <luto@...capital.net>


I know this has been in the tip tree --- when do you think this will go 
Linus tree? In the 4.4 timeframe?

Xen 32-bit PV guests are broken without this.


Thanks.
-boris

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