Re: [PATCH v3 73/75] x86/sev-es: Support CPU offline/online

Borislav Petkov
2020-06-03T09:54:37Z

On Tue, Apr 28, 2020 at 05:17:23PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> Add a play_dead handler when running under SEV-ES. This is needed
> because the hypervisor can't deliver an SIPI request to restart the AP.
> Instead the kernel has to issue a VMGEXIT to halt the VCPU. When the
> hypervisor would deliver and SIPI is wakes up the VCPU instead.

That last sentence needs fixing.

Also, that explanation belongs as comment over sev_es_ap_hlt_loop()
because commit messages are not that easy to find.

> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> arch/x86/include/uapi/asm/svm.h | 1 +
> arch/x86/kernel/sev-es.c | 58 +++++++++++++++++++++++++++++++++
> 2 files changed, 59 insertions(+)
>
> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
> index a19ce9681ec2..20a05839dd9a 100644
> --- a/arch/x86/include/uapi/asm/svm.h
> +++ b/arch/x86/include/uapi/asm/svm.h
> @@ -84,6 +84,7 @@
> /* SEV-ES software-defined VMGEXIT events */
> #define SVM_VMGEXIT_MMIO_READ 0x80000001
> #define SVM_VMGEXIT_MMIO_WRITE 0x80000002
> +#define SVM_VMGEXIT_AP_HLT_LOOP 0x80000004
> #define SVM_VMGEXIT_AP_JUMP_TABLE 0x80000005
> #define SVM_VMGEXIT_SET_AP_JUMP_TABLE 0
> #define SVM_VMGEXIT_GET_AP_JUMP_TABLE 1
> diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
> index 28725c38e6fb..00a5d0483730 100644
> --- a/arch/x86/kernel/sev-es.c
> +++ b/arch/x86/kernel/sev-es.c
> @@ -32,6 +32,8 @@
> #include <asm/processor.h>
> #include <asm/traps.h>
> #include <asm/svm.h>
> +#include <asm/smp.h>
> +#include <asm/cpu.h>
>
> #define DR7_RESET_VALUE 0x400
>
> @@ -448,6 +450,60 @@ static bool __init sev_es_setup_ghcb(void)
> return true;
> }
>
> +#ifdef CONFIG_HOTPLUG_CPU
> +static void sev_es_ap_hlt_loop(void)
> +{
> + struct ghcb_state state;
> + struct ghcb *ghcb;
> +
> + ghcb = sev_es_get_ghcb(&state);
> +
> + while (true) {
> + vc_ghcb_invalidate(ghcb);
> + ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_AP_HLT_LOOP);
> + ghcb_set_sw_exit_info_1(ghcb, 0);
> + ghcb_set_sw_exit_info_2(ghcb, 0);
> +
> + sev_es_wr_ghcb_msr(__pa(ghcb));
> + VMGEXIT();
> +
> + /* Wakup Signal? */

"Wakeup"

> + if (ghcb_is_valid_sw_exit_info_2(ghcb) &&
> + ghcb->save.sw_exit_info_2 != 0)

No need for the "!= 0".

> + break;
> + }
> +
> + sev_es_put_ghcb(&state);
> +}

...

--
Regards/Gruss,
Boris.