[PATCH v15 10/11] arm64: entry: Convert to generic entry

[Mark Rutland]

On Thu, Jul 02, 2026 at 01:34:34PM +0100, Will Deacon wrote:
> On Wed, Jun 24, 2026 at 04:32:17PM +0100, Ada Couprie Diaz wrote:
> > On 11/05/2026 10:21, Jinjie Ruan wrote:
> > > 3. Architecture-Specific Hooks (asm/entry-common.h):
> > > - Implement arch_ptrace_report_syscall_entry() and _exit() by
> > >    porting the existing arm64 logic to the generic interface.
> > > 
> > > - Add arch_syscall_is_vdso_sigreturn() to asm/syscall.h to
> > >    support Syscall User Dispatch (SUD).
> > Related to the above : I feel this is missing an important information.
> > Given that SUD is only controlled by `CONFIG_GENERIC_ENTRY`,
> > converting to generic entry _requires_ supporting SUD, so we do it here.
> > I think this would be important to mention, as I otherwise felt like this
> > change did not belong in this patch.
> > 
> > General question that follows : does it make sense to require an arch
> > to support Syscall User Dispatch to be able to convert to generic entry ?
> > (I assume not really, given that only `arch_syscall_is_vdso_sigreturn()` is
> > required on the arch side, but I am curious)
> 
> I think SUD should be separated from generic entry. I'm certainly keen
> on the latter for arm64 and far less interested in the former. See this
> series from Gregory:
> 
> https://lore.kernel.org/all/20260627205551.769684-1-gourry@gourry.net/

Agreed.

I see Gregory mentions some security concerns, and I think there are a
number of architecture-specific ABI concerns (e.g. how arm64's SVC
immediate gets handled), so I'm not keen to rush into supporting
SYSCALL_USER_DISPATCH.

I think what we want is:

(1) SYSCALL_USER_DISPATCH depends on GENERIC_ENTRY, as in Gregory's
    series.

(2) SYSCALL_USER_DISPATCH depends on some new
    ARCH_SUPPORTS_SYSCALL_USER_DISPATCH, such that it an architecture
    can implement GENERIC_ENTRY *without* being forced to implement
    SYSCALL_USER_DISPATCH.

(3) For now, we implement GENERIC_ENTRY for arm64 *without*
    ARCH_SUPPORTS_SYSCALL_USER_DISPATCH.

That way, we can focus on the core GENERIC_ENTRY support for arm64, and
address the inevitable fallout of that *before* we have to work through
all the concerns with SYSCALL_USER_DISPATCH.

Mark.