Re: [PATCH v6 27/76] x86/sev-es: Add CPUID handling to #VC handler

[Joerg Roedel]

On Thu, Aug 27, 2020 at 06:48:10PM -0400, Arvind Sankar wrote:
> On Mon, Aug 24, 2020 at 10:54:22AM +0200, Joerg Roedel wrote:
> > From: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > 
> > Handle #VC exceptions caused by CPUID instructions. These happen in
> > early boot code when the KASLR code checks for RDTSC.
> > 
> > Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > [ jroedel@xxxxxxx: Adapt to #VC handling framework ]
> > Co-developed-by: Joerg Roedel <jroedel@xxxxxxx>
> > Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> > Link: https://lore.kernel.org/r/20200724160336.5435-27-joro@xxxxxxxxxx
> > ---
> > +
> > +static enum es_result vc_handle_cpuid(struct ghcb *ghcb,
> > +				      struct es_em_ctxt *ctxt)
> > +{
> > +	struct pt_regs *regs = ctxt->regs;
> > +	u32 cr4 = native_read_cr4();
> > +	enum es_result ret;
> > +
> > +	ghcb_set_rax(ghcb, regs->ax);
> > +	ghcb_set_rcx(ghcb, regs->cx);
> > +
> > +	if (cr4 & X86_CR4_OSXSAVE)
> 
> Will this ever happen? trampoline_32bit_src will clear CR4 except for
> PAE and possibly LA57, no?

This same code is later re-used in the runtime handler and there the
check is needed :)

Regards,

	Joerg