linux-kernel - Re: [PATCH] x86/paravirt: convert simple paravirt functions to asm

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Date:   Thu, 16 Mar 2023 17:50:17 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        virtualization@...ts.linux-foundation.org,
        "Srivatsa S. Bhat (VMware)" <srivatsa@...il.mit.edu>,
        Alexey Makhalov <amakhalov@...are.com>,
        VMware PV-Drivers Reviewers <pv-drivers@...are.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/paravirt: convert simple paravirt functions to asm

On Wed, Mar 08, 2023 at 04:42:10PM +0100, Juergen Gross wrote:
> All functions referenced via __PV_IS_CALLEE_SAVE() need to be assembler
> functions, as those functions calls are hidden from gcc. In case the
> kernel is compiled with "-fzero-call-used-regs" the compiler will
> clobber caller-saved registers at the end of C functions, which will
> result in unexpectedly zeroed registers at the call site of the
> related paravirt functions.
> 
> Replace the C functions with DEFINE_PARAVIRT_ASM() constructs using
> the same instructions as the related paravirt calls in the
> PVOP_ALT_[V]CALLEE*() macros.
> 
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  arch/x86/include/asm/paravirt_types.h |  8 +++++++-
>  arch/x86/kernel/paravirt.c            | 27 ++++++---------------------
>  2 files changed, 13 insertions(+), 22 deletions(-)

objtool's not happy with this for whatever reason. I'll look later as to
why. .config is allmodconfig with this patch ontop of tip:x86/paravirt:

vmlinux.o: warning: objtool: pv_ops[31]: pv_native_irq_disable
vmlinux.o: warning: objtool: default_idle+0x1e: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[31]: pv_native_irq_disable
vmlinux.o: warning: objtool: mwait_idle+0x5d: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[31]: pv_native_irq_disable
vmlinux.o: warning: objtool: cpu_idle_poll.isra.0+0x94: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[31]: pv_native_irq_disable
vmlinux.o: warning: objtool: intel_idle_irq+0xab: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[31]: pv_native_irq_disable
vmlinux.o: warning: objtool: acpi_safe_halt+0x2a: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[31]: pv_native_irq_disable
vmlinux.o: warning: objtool: poll_idle+0x86: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[42]: pv_native_read_cr2
vmlinux.o: warning: objtool: exc_double_fault+0x3b: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[42]: pv_native_read_cr2
vmlinux.o: warning: objtool: exc_nmi+0x188: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[30]: pv_native_save_fl
vmlinux.o: warning: objtool: __sev_put_ghcb+0x11: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[30]: pv_native_save_fl
vmlinux.o: warning: objtool: __sev_get_ghcb+0x13: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[42]: pv_native_read_cr2
vmlinux.o: warning: objtool: exc_page_fault+0x1e: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[30]: pv_native_save_fl
vmlinux.o: warning: objtool: lockdep_hardirqs_on+0xd0: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[30]: pv_native_save_fl
vmlinux.o: warning: objtool: lockdep_hardirqs_off+0xe7: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[30]: pv_native_save_fl
vmlinux.o: warning: objtool: look_up_lock_class+0x52: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[32]: pv_native_irq_enable
vmlinux.o: warning: objtool: lock_is_held_type+0x143: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[30]: pv_native_save_fl
vmlinux.o: warning: objtool: ct_kernel_enter.constprop.0+0x37: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[32]: pv_native_irq_enable
vmlinux.o: warning: objtool: ct_idle_exit+0x51: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[30]: pv_native_save_fl
vmlinux.o: warning: objtool: ct_idle_enter+0xe: call to {dynamic}() leaves .noinstr.text section
vmlinux.o: warning: objtool: pv_ops[30]: pv_native_save_fl
vmlinux.o: warning: objtool: check_preemption_disabled+0x4c: call to {dynamic}() leaves .noinstr.text section

-- 
Regards/Gruss,
    Boris.

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