Re: [PATCH v2 01/10] x86/boot: Drop pointless re-implementation of panic()

[Kiryl Shutsemau <kirill@shutemov.name>]

On Wed, Sep 09, 2026 at 10:43:23PM +0200, Ard Biesheuvel wrote:
> 
> On Wed, 9 Sep 2026, at 21:14, Borislav Petkov wrote:
> > On Wed, Sep 09, 2026 at 01:55:32PM +0200, Ard Biesheuvel wrote:
> >> From: Ard Biesheuvel <ardb@kernel.org>
> >> 
> >> The decompressor has its own implementation of panic(), which is based
> >> on the vsnprintf() routine provided by the EFI stub.
> >> 
> >> Relying on the EFI stub from code that does not execute in the context
> >> of the EFI boot services is a bad idea. It is also completely pointless
> >> in this case, given that the only user of this version of panic() only
> >> passes a compile time constant string, without any printf conversions.
> >> 
> >> So use error() instead of panic() in that case, and drop the panic()
> >> implementation entirely. This is needed so that the EFI stub's
> >> vsnprintf() can be modified in a manner that is incompatible with the
> >> expectations of this caller.
> >> 
> >> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> >> ---
> >>  arch/x86/boot/compressed/error.c | 19 -------------------
> >>  arch/x86/boot/compressed/error.h |  1 -
> >>  arch/x86/boot/compressed/mem.c   |  2 +-
> >>  3 files changed, 1 insertion(+), 21 deletions(-)
> >> 
> >> diff --git a/arch/x86/boot/compressed/error.c b/arch/x86/boot/compressed/error.c
> >> index 19a8251de506..ce5ed7d8265e 100644
> >> --- a/arch/x86/boot/compressed/error.c
> >> +++ b/arch/x86/boot/compressed/error.c
> >> @@ -22,22 +22,3 @@ void error(char *m)
> >>  	while (1)
> >>  		asm("hlt");
> >>  }
> >> -
> >> -/* EFI libstub  provides vsnprintf() */
> >> -#ifdef CONFIG_EFI_STUB
> >> -void panic(const char *fmt, ...)
> >
> > So this thing appeared magically in v8 of the TDX unaccepted memory patches
> > and I don't think we questioned it back then.
> >
> > v7's tdx_accept_memory() does error():
> >
> > https://lore.kernel.org/all/20220614120231.48165-15-kirill.shutemov@linux.intel.com/
> >
> > and v8 started doing panic():
> >
> > +void tdx_accept_memory(phys_addr_t start, phys_addr_t end)
> > +{
> > +	if (!tdx_enc_status_changed_phys(start, end, true))
> > +		panic("Accepting memory failed: %#llx-%#llx\n",  start, end);
> > +}
> >
> > https://lore.kernel.org/all/20221207014933.8435-15-kirill.shutemov@linux.intel.com/
> >
> > and it switched to it being a vsnprintf() wrapper because it wanted to dump
> > start and end perhaps.
> >
> > But then it ended up dropping the params in v13 and landed upstream with
> > a single string as an argument.
> >
> > Anyway, adding Kiryl/Kirill for comment and leaving in the rest for reference.
> >
> 
> Looking at that v13, it seems the panic() call was added to
> arch/x86/coco/tdx/tdx-shared.c, which was shared between the kernel proper and
> the decompressorat the time, and so a panic() implementation was needed in the
> decompressor too. But that is no longer the case.

Right. I don't mind dropping this panic() from the decompressor. The
range was already gone since v13 and I never saw the error trigger
anyway.

Acked-by: Kiryl Shutsemau (Meta) <kas@kernel.org>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov