Re: [PATCH 08/10] x86/tdx: Unify TDX_HYPERCALL and TDX_MODULE_CALL assembly

["Huang, Kai" <kai.huang@intel.com>]

On Mon, 2023-07-17 at 07:58 +0000, Huang, Kai wrote:
> > On 17.07.23 г. 9:35 ч., Huang, Kai wrote:
> > > 
> > > > > +/* Called from __tdx_hypercall() for unrecoverable failure */
> > > > > +static noinstr void __tdx_hypercall_failed(void) {
> > > > > +	instrumentation_begin();
> > > > > +	panic("TDVMCALL failed. TDX module bug?"); }
> > > > 
> > > > So what's the deal with this instrumentation here. The instruction is
> > > > noinstr, so you want to make just the panic call itself
> > > > instrumentable?, if so where's the instrumentation_end() cal;?No
> > > > instrumentation_end() call. Actually is this complexity really worth it for the
> > failure case?
> > > > 
> > > > AFAICS there is a single call site for __tdx_hypercall_failed so why
> > > > noot call panic() directly ?
> > > 
> > > W/o this patch, the __tdx_hypercall_failed() is called from the
> > > TDX_HYPERCALL assembly, which is in .noinstr.text, and
> > > 'instrumentation_begin()' was needed to avoid the build warning I suppose.
> > > 
> > > However now with this patch __tdx_hypercall_failed() is called from
> > > __tdx_hypercall() which is a C function w/o 'noinstr' annotation, thus
> > > I believe
> > > instrumentation_begin() and 'noinstr' annotation are not needed anymore.
> > > 
> > > I didn't notice this while moving this function around and my kernel
> > > build test didn't warn me about this.  I'll change in next version.
> > > 
> > > In fact, perhaps this patch perhaps is too big for review.  I will
> > > also try to split it to smaller ones.
> > 
> > Can't you simply call panic() directly? Less going around the code while someone
> > is reading it?
> 
> I can and will do.

After rebasing to the latest TDX code, I found we should keep the
__tdx_hypercall_failed().  The reason is both the core-kernel (vmlinux) and the
compressed code need the __tdx_hypercall() implementation.  Implementing the
__tdx_hypercall_failed() in both core-kernel and compressed code separately
allows the __tdx_hypercall() to be shared by both code, otherwise both of them
need to implement their own __tdx_hypercall().

Note __tdx_hypercall_failed() in the vmlinux calls panic(), but the one in the
compressed code calls error().