Re: [PATCH v1 21/26] crypto: ccp: Add panic notifier for SEV/SNP firmware shutdown on kdump

Borislav Petkov
2024-01-21T11:49:55Z

On Sat, Dec 30, 2023 at 10:19:49AM -0600, Michael Roth wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
>
> Add a kdump safe version of sev_firmware_shutdown() registered as a
> crash_kexec_post_notifier, which is invoked during panic/crash to do
> SEV/SNP shutdown. This is required for transitioning all IOMMU pages
> to reclaim/hypervisor state, otherwise re-init of IOMMU pages during
> crashdump kernel boot fails and panics the crashdump kernel. This
> panic notifier runs in atomic context, hence it ensures not to
> acquire any locks/mutexes and polls for PSP command completion
> instead of depending on PSP command completion interrupt.
>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> [mdr: remove use of "we" in comments]
> Signed-off-by: Michael Roth <michael.roth@amd.com>

Cleanups ontop, see if the below works too. Especially:

* I've zapped the WBINVD before the TMR pages are freed because
__sev_snp_shutdown_locked() will WBINVD anyway.

* The mutex_is_locked() check in snp_shutdown_on_panic() is silly
because the panic notifier runs on one CPU anyway.

Thx.

---

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 435ba9bc4510..27323203e593 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -227,6 +227,7 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct sn
void snp_accept_memory(phys_addr_t start, phys_addr_t end);
u64 snp_get_unsupported_features(u64 status);
u64 sev_get_status(void);
+void kdump_sev_callback(void);
#else
static inline void sev_es_ist_enter(struct pt_regs *regs) { }
static inline void sev_es_ist_exit(void) { }
@@ -255,6 +256,7 @@ static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *in
static inline void snp_accept_memory(phys_addr_t start, phys_addr_t end) { }
static inline u64 snp_get_unsupported_features(u64 status) { return 0; }
static inline u64 sev_get_status(void) { return 0; }
+static inline void kdump_sev_callback(void) { }
#endif

#ifdef CONFIG_KVM_AMD_SEV
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 23ede774d31b..64ae3a1e5c30 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -40,6 +40,7 @@
#include <asm/intel_pt.h>
#include <asm/crash.h>
#include <asm/cmdline.h>
+#include <asm/sev.h>

/* Used while preparing memory map entries for second kernel */
struct crash_memmap_data {
@@ -59,12 +60,7 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
*/
cpu_emergency_stop_pt();

- /*
- * for SNP do wbinvd() on remote CPUs to
- * safely do SNP_SHUTDOWN on the local CPU.
- */
- if (cpu_feature_enabled(X86_FEATURE_SEV_SNP))
- wbinvd();
+ kdump_sev_callback();

disable_local_APIC();
}
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index c67285824e82..dbb2cc6b5666 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2262,3 +2262,13 @@ static int __init snp_init_platform_device(void)
return 0;
}
device_initcall(snp_init_platform_device);
+
+void kdump_sev_callback(void)
+{
+ /*
+ * Do wbinvd() on remote CPUs when SNP is enabled in order to
+ * safely do SNP_SHUTDOWN on the the local CPU.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+ wbinvd();
+}
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 598878e760bc..c342e5e54e45 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -161,7 +161,6 @@ static int sev_wait_cmd_ioc(struct sev_device *sev,

udelay(10);
}
-
return -ETIMEDOUT;
}

@@ -1654,7 +1653,7 @@ static int sev_update_firmware(struct device *dev)
return ret;
}

-static int __sev_snp_shutdown_locked(int *error, bool in_panic)
+static int __sev_snp_shutdown_locked(int *error, bool panic)
{
struct sev_device *sev = psp_master->sev_data;
struct sev_data_snp_shutdown_ex data;
@@ -1673,7 +1672,7 @@ static int __sev_snp_shutdown_locked(int *error, bool in_panic)
* In that case, a wbinvd() is done on remote CPUs via the NMI
* callback, so only a local wbinvd() is needed here.
*/
- if (!in_panic)
+ if (!panic)
wbinvd_on_all_cpus();
else
wbinvd();
@@ -2199,26 +2198,13 @@ int sev_dev_init(struct psp_device *psp)
return ret;
}

-static void __sev_firmware_shutdown(struct sev_device *sev, bool in_panic)
+static void __sev_firmware_shutdown(struct sev_device *sev, bool panic)
{
int error;

__sev_platform_shutdown_locked(NULL);

if (sev_es_tmr) {
- /*
- * The TMR area was encrypted, flush it from the cache
- *
- * If invoked during panic handling, local interrupts are
- * disabled and all CPUs are stopped, so wbinvd_on_all_cpus()
- * can't be used. In that case, wbinvd() is done on remote CPUs
- * via the NMI callback, so a local wbinvd() is sufficient here.
- */
- if (!in_panic)
- wbinvd_on_all_cpus();
- else
- wbinvd();
-
__snp_free_firmware_pages(virt_to_page(sev_es_tmr),
get_order(sev_es_tmr_size),
true);
@@ -2237,7 +2223,7 @@ static void __sev_firmware_shutdown(struct sev_device *sev, bool in_panic)
snp_range_list = NULL;
}

- __sev_snp_shutdown_locked(&error, in_panic);
+ __sev_snp_shutdown_locked(&error, panic);
}

static void sev_firmware_shutdown(struct sev_device *sev)
@@ -2262,26 +2248,18 @@ void sev_dev_destroy(struct psp_device *psp)
psp_clear_sev_irq_handler(psp);
}

-static int sev_snp_shutdown_on_panic(struct notifier_block *nb,
- unsigned long reason, void *arg)
+static int snp_shutdown_on_panic(struct notifier_block *nb,
+ unsigned long reason, void *arg)
{
struct sev_device *sev = psp_master->sev_data;

- /*
- * Panic callbacks are executed with all other CPUs stopped,
- * so don't wait for sev_cmd_mutex to be released since it
- * would block here forever.
- */
- if (mutex_is_locked(&sev_cmd_mutex))
- return NOTIFY_DONE;
-
__sev_firmware_shutdown(sev, true);

return NOTIFY_DONE;
}

-static struct notifier_block sev_snp_panic_notifier = {
- .notifier_call = sev_snp_shutdown_on_panic,
+static struct notifier_block snp_panic_notifier = {
+ .notifier_call = snp_shutdown_on_panic,
};

int sev_issue_cmd_external_user(struct file *filep, unsigned int cmd,
@@ -2322,7 +2300,7 @@ void sev_pci_init(void)
"-SNP" : "", sev->api_major, sev->api_minor, sev->build);

atomic_notifier_chain_register(&panic_notifier_list,
- &sev_snp_panic_notifier);
+ &snp_panic_notifier);
return;

err:
@@ -2339,5 +2317,5 @@ void sev_pci_exit(void)
sev_firmware_shutdown(sev);

atomic_notifier_chain_unregister(&panic_notifier_list,
- &sev_snp_panic_notifier);
+ &snp_panic_notifier);
}

--
Regards/Gruss,
Boris.