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Re: [Xen-devel] [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@xxxxxxxxxx>
Suggested-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>

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.


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