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Date: Fri, 13 Nov 2015 20:23:48 -0500 From: Boris Ostrovsky <boris.ostrovsky@...cle.com> To: Andy Lutomirski <luto@...capital.net> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, David Vrabel <david.vrabel@...rix.com>, xen-devel <xen-devel@...ts.xen.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Andrew Lutomirski <luto@...nel.org> Subject: Re: [PATCH] xen/x86: Adjust stack pointer in xen_sysexit On 11/13/2015 06:26 PM, Andy Lutomirski wrote: > On Fri, Nov 13, 2015 at 3:18 PM, Boris Ostrovsky > <boris.ostrovsky@...cle.com> 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). >> >> We need to adjust it so that subsequent xen_iret can use it. > I'm wondering if this should be more straightforward: > > movq %rsp, %rdi > call do_fast_syscall_32 > testl %eax, %eax > jz .Lsyscall_32_done > > /* Opportunistic SYSRET */ > sysret32_from_system_call: > XEN_DO_SYSRET32 > > where XEN_DO_SYSRET32 is a simple pv op that, on Xen, jumps to a > variant of Xen's iret path that knows that the fast path is okay. This patch is for 32-bit kernel. I actually haven't looked at compat code (probably because our tests don't try that), I need to do that too. As for XEN_DO_SYSRET32 --- we'd presumably need to have a nop for baremetal otherwise current paravirt op will use native_usergs_sysret32 (for compat code). Which means a new pv_op, I think. -boris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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