On 09.03.23 14:39, Borislav Petkov wrote:
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@xxxxxxxx> --- arch/x86/include/asm/paravirt_types.h | 8 +++++++- arch/x86/kernel/paravirt.c | 27 ++++++--------------------- 2 files changed, 13 insertions(+), 22 deletions(-)Right, works with my particular reproducer. Turning them into asm prevents the compiler from doing the callee-clobbered zeroing and that's fine as this whole paravirt gunk is hiding the "CALL" insn from it and you putting them in asm is in line with this. And a negative diffstat.. So yeah, I'll queue it soon unless someone objects.
Thanks.
Long term, I think we should continue switching all that pv stuff to using the alternatives.
The "normal" cases not using alternatives should rather be switched to static calls. Whether it is possible to mix a static call with alternatives needs to be evaluated. Juergen
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