Re: [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call

2020-12-02 Thread Borislav Petkov
On Wed, Dec 02, 2020 at 03:48:21PM +0100, Jürgen Groß wrote: > I wanted to avoid the additional NOPs for the bare metal case. Yeah, in that case it gets optimized to a single NOP: [0.176692] SMP alternatives: 81a00068: [0:5) optimized NOPs: 0f 1f 44 00 00 which is nopl

Re: [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call

2020-12-02 Thread Jürgen Groß
On 02.12.20 13:32, Borislav Petkov wrote: On Fri, Nov 20, 2020 at 12:46:22PM +0100, Juergen Gross wrote: @@ -123,12 +115,15 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL) * Try to use SYSRET instead of IRET if we're returning to * a completely clean 64-bit

Re: [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call

2020-12-02 Thread Borislav Petkov
On Fri, Nov 20, 2020 at 12:46:22PM +0100, Juergen Gross wrote: > @@ -123,12 +115,15 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, > SYM_L_GLOBAL) >* Try to use SYSRET instead of IRET if we're returning to >* a completely clean 64-bit userspace context. If we're not, >

[PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call

2020-11-20 Thread Juergen Gross
USERGS_SYSRET64 is used to return from a syscall via sysret, but a Xen PV guest will nevertheless use the iret hypercall, as there is no sysret PV hypercall defined. So instead of testing all the prerequisites for doing a sysret and then mangling the stack for Xen PV again for doing an iret just