Re: [PATCH v9 20/43] x86/sev: Use SEV-SNP AP creation to start secondary CPUs

Borislav Petkov
2022-02-03T06:50:47Z

On Fri, Jan 28, 2022 at 11:17:41AM -0600, Brijesh Singh wrote:
> @@ -822,6 +842,236 @@ void snp_set_memory_private(unsigned long vaddr, unsigned int npages)
> pvalidate_pages(vaddr, npages, true);
> }
>
> +static int snp_set_vmsa(void *va, bool vmsa)
> +{
> + u64 attrs;
> +
> + /*
> + * Running at VMPL0 allows the kernel to change the VMSA bit for a page
> + * using the RMPADJUST instruction. However, for the instruction to
> + * succeed it must target the permissions of a lesser privileged

"lesser privileged/higher number VMPL level"

so that it is perfectly clear what this means.

> + * VMPL level, so use VMPL1 (refer to the RMPADJUST instruction in the
> + * AMD64 APM Volume 3).
> + */
> + attrs = 1;
> + if (vmsa)
> + attrs |= RMPADJUST_VMSA_PAGE_BIT;
> +
> + return rmpadjust((unsigned long)va, RMP_PG_SIZE_4K, attrs);
> +}

...

> +static int wakeup_cpu_via_vmgexit(int apic_id, unsigned long start_ip)
> +{
> + struct sev_es_save_area *cur_vmsa, *vmsa;
> + struct ghcb_state state;
> + unsigned long flags;
> + struct ghcb *ghcb;
> + u8 sipi_vector;
> + int cpu, ret;
> + u64 cr4;
> +
> + /*
> + * SNP-SNP AP creation requires that the hypervisor must support SEV-SNP
^^^^^^^

See what I mean? :-)

That marketing has brainwashed y'all.

> + * feature. The SEV-SNP feature check is already performed, so just check
> + * for the AP_CREATION feature flag.
> + */

Let's clean this one:

/*
* The hypervisor SNP feature support check has happened earlier, just check
* the AP_CREATION one here.
*/

> + if (!(sev_hv_features & GHCB_HV_FT_SNP_AP_CREATION))
> + return -EOPNOTSUPP;
> +
> + /*
> + * Verify the desired start IP against the known trampoline start IP
> + * to catch any future new trampolines that may be introduced that
> + * would require a new protected guest entry point.
> + */
> + if (WARN_ONCE(start_ip != real_mode_header->trampoline_start,
> + "Unsupported SEV-SNP start_ip: %lx\n", start_ip))
> + return -EINVAL;
> +
> + /* Override start_ip with known protected guest start IP */
> + start_ip = real_mode_header->sev_es_trampoline_start;

Yah, I'd like to get rid of that ->sev_es_trampoline_start and use the
normal ->trampoline_start. TDX is introducing a third one even and
they're all mutually-exclusive u32 values.

...

--
Regards/Gruss,
Boris.