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

[Arvind Sankar]

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?

> +		/* Safe to read xcr0 */
> +		ghcb_set_xcr0(ghcb, xgetbv(XCR_XFEATURE_ENABLED_MASK));
> +	else
> +		/* xgetbv will cause #GP - use reset value for xcr0 */
> +		ghcb_set_xcr0(ghcb, 1);
> +
> +	ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_CPUID, 0, 0);
> +	if (ret != ES_OK)
> +		return ret;
> +
> +	if (!(ghcb_rax_is_valid(ghcb) &&
> +	      ghcb_rbx_is_valid(ghcb) &&
> +	      ghcb_rcx_is_valid(ghcb) &&
> +	      ghcb_rdx_is_valid(ghcb)))
> +		return ES_VMM_ERROR;
> +
> +	regs->ax = ghcb->save.rax;
> +	regs->bx = ghcb->save.rbx;
> +	regs->cx = ghcb->save.rcx;
> +	regs->dx = ghcb->save.rdx;
> +
> +	return ES_OK;
> +}
> -- 
> 2.28.0
>