Re: [PATCH 05/39] x86/entry/32: Unshare NMI return path

[Andy Lutomirski]

> On Jul 11, 2018, at 4:29 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote:
> 
> From: Joerg Roedel <jroedel@xxxxxxx>
> 
> NMI will no longer use most of the shared return path,
> because NMI needs special handling when the CR3 switches for
> PTI are added.

Why?  What would go wrong?

How many return-to-usermode paths will we have?  64-bit has only one.

> This patch prepares for that.
> 
> Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> ---
> arch/x86/entry/entry_32.S | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
> index d35a69a..571209e 100644
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -1017,7 +1017,7 @@ ENTRY(nmi)
> 
>    /* Not on SYSENTER stack. */
>    call    do_nmi
> -    jmp    .Lrestore_all_notrace
> +    jmp    .Lnmi_return
> 
> .Lnmi_from_sysenter_stack:
>    /*
> @@ -1028,7 +1028,11 @@ ENTRY(nmi)
>    movl    PER_CPU_VAR(cpu_current_top_of_stack), %esp
>    call    do_nmi
>    movl    %ebx, %esp
> -    jmp    .Lrestore_all_notrace
> +
> +.Lnmi_return:
> +    CHECK_AND_APPLY_ESPFIX
> +    RESTORE_REGS 4
> +    jmp    .Lirq_return
> 
> #ifdef CONFIG_X86_ESPFIX32
> .Lnmi_espfix_stack:
> -- 
> 2.7.4
>