Re: [RFC v2 01/17] x86/apic: Add new driver for Secure AVIC

Borislav Petkov
2025-03-20T15:52:28Z

On Wed, Feb 26, 2025 at 02:35:09PM +0530, Neeraj Upadhyay wrote:
> +config AMD_SECURE_AVIC
> + bool "AMD Secure AVIC"
> + depends on X86_X2APIC
> + help
> + This enables AMD Secure AVIC support on guests that have this feature.

"Enable this to get ..."

> + AMD Secure AVIC provides hardware acceleration for performance sensitive
> + APIC accesses and support for managing guest owned APIC state for SEV-SNP
> + guests. Secure AVIC does not support xapic mode. It has functional
> + dependency on x2apic being enabled in the guest.
> +
> + If you don't know what to do here, say N.
> +
> config X86_POSTED_MSI
> bool "Enable MSI and MSI-x delivery by posted interrupts"
> depends on X86_64 && IRQ_REMAP
> @@ -1557,6 +1570,7 @@ config AMD_MEM_ENCRYPT
> select X86_MEM_ENCRYPT
> select UNACCEPTED_MEMORY
> select CRYPTO_LIB_AESGCM
> + select AMD_SECURE_AVIC

AMD_MEM_ENCRYPT doesn't absolutely need AMD_SECURE_AVIC so this can go.

> help
> Say yes to enable support for the encryption of system memory.
> This requires an AMD processor that supports Secure Memory

...

> +static void x2apic_savic_send_IPI(int cpu, int vector)
> +{
> + u32 dest = per_cpu(x86_cpu_to_apicid, cpu);
> +
> + /* x2apic MSRs are special and need a special fence: */
> + weak_wrmsr_fence();
> + __x2apic_send_IPI_dest(dest, vector, APIC_DEST_PHYSICAL);
> +}
> +
> +static void

Unnecessary line break.

> +__send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest)
> +{
> + unsigned long query_cpu;
> + unsigned long this_cpu;
> + unsigned long flags;
> +
> + /* x2apic MSRs are special and need a special fence: */
> + weak_wrmsr_fence();
> +
> + local_irq_save(flags);
> +
> + this_cpu = smp_processor_id();
> + for_each_cpu(query_cpu, mask) {
> + if (apic_dest == APIC_DEST_ALLBUT && this_cpu == query_cpu)
> + continue;
> + __x2apic_send_IPI_dest(per_cpu(x86_cpu_to_apicid, query_cpu),
> + vector, APIC_DEST_PHYSICAL);
> + }
> + local_irq_restore(flags);
> +}
> +
> +static void x2apic_savic_send_IPI_mask(const struct cpumask *mask, int vector)
> +{
> + __send_IPI_mask(mask, vector, APIC_DEST_ALLINC);
> +}
> +
> +static void x2apic_savic_send_IPI_mask_allbutself(const struct cpumask *mask, int vector)
> +{
> + __send_IPI_mask(mask, vector, APIC_DEST_ALLBUT);
> +}
> +
> +static int x2apic_savic_probe(void)
> +{
> + if (!cc_platform_has(CC_ATTR_SNP_SECURE_AVIC))
> + return 0;
> +
> + if (!x2apic_mode) {
> + pr_err("Secure AVIC enabled in non x2APIC mode\n");
> + snp_abort();
> + }
> +
> + pr_info("Secure AVIC Enabled\n");

That's not necessary.

Actually, you could figure out why that

pr_info("Switched APIC routing to: %s\n", driver->name);

doesn't come out in current kernels anymore:

$ dmesg | grep -i "switched apic"
$

and fix that as a separate patch.

Looks like it broke in 6.10 or so:

$ grep -E "Switched APIC" *
04-rc7+:Switched APIC routing to physical flat.
05-rc1+:Switched APIC routing to physical flat.
05-rc2+:Switched APIC routing to physical flat.
05-rc3+:Switched APIC routing to physical flat.
05-rc4+:APIC: Switched APIC routing to: physical flat
05-rc6+:Switched APIC routing to physical flat.
06-rc4+:APIC: Switched APIC routing to: physical flat
06-rc6+:APIC: Switched APIC routing to: physical flat
07-0+:APIC: Switched APIC routing to: physical flat
07-rc1+:APIC: Switched APIC routing to: physical flat
07-rc7+:APIC: Switched APIC routing to: physical flat
08-rc1+:APIC: Switched APIC routing to: physical flat
08-rc3+:APIC: Switched APIC routing to: physical flat
08-rc6+:APIC: Switched APIC routing to: physical flat
08-rc7+:APIC: Switched APIC routing to: physical flat
09-rc7+:APIC: Switched APIC routing to: physical flat
10-rc1+:APIC: Switched APIC routing to: physical flat
10-rc6+:APIC: Switched APIC routing to: physical flat
<--- EOF

Thx.

--
Regards/Gruss,
Boris.