[PATCH v2 20/25] crypto: ccp: Add panic notifier for SEV/SNP firmware shutdown on kdump

Michael Roth
2024-01-26T04:44:43Z

From: Ashish Kalra <ashish.kalra@amd.com>

Add a kdump safe version of sev_firmware_shutdown() and register it as a
crash_kexec_post_notifier so it will be 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>
---
arch/x86/include/asm/sev.h | 2 +
arch/x86/kernel/crash.c | 3 +
arch/x86/kernel/sev.c | 10 ++++
arch/x86/virt/svm/sev.c | 6 ++
drivers/crypto/ccp/sev-dev.c | 111 +++++++++++++++++++++++++----------
5 files changed, 102 insertions(+), 30 deletions(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 435ba9bc4510..b3ba32c6fc9f 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 b6b044356f1b..d184c29398db 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 {
@@ -59,6 +60,8 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
*/
cpu_emergency_stop_pt();

+ kdump_sev_callback();
+
disable_local_APIC();
}

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 1ec753331524..002af6c30601 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2265,3 +2265,13 @@ 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 local CPU.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+ wbinvd();
+}
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 649ac1bb6b0e..3d33b75b4606 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -216,6 +216,12 @@ static int __init snp_rmptable_init(void)

cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/rmptable_init:online", __snp_enable, NULL);

+ /*
+ * Setting crash_kexec_post_notifiers to 'true' to ensure that SNP panic
+ * notifier is invoked to do SNP IOMMU shutdown before kdump.
+ */
+ crash_kexec_post_notifiers = true;
+
return 0;

nosnp:
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index d26bff55ec93..9a395f0f9b10 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -21,6 +21,7 @@
#include <linux/hw_random.h>
#include <linux/ccp.h>
#include <linux/firmware.h>
+#include <linux/panic_notifier.h>
#include <linux/gfp.h>
#include <linux/cpufeature.h>
#include <linux/fs.h>
@@ -143,6 +144,25 @@ static int sev_wait_cmd_ioc(struct sev_device *sev,
{
int ret;

+ /*
+ * If invoked during panic handling, local interrupts are disabled,
+ * so the PSP command completion interrupt can't be used. Poll for
+ * PSP command completion instead.
+ */
+ if (irqs_disabled()) {
+ unsigned long timeout_usecs = (timeout * USEC_PER_SEC) / 10;
+
+ /* Poll for SEV command completion: */
+ while (timeout_usecs--) {
+ *reg = ioread32(sev->io_regs + sev->vdata->cmdresp_reg);
+ if (*reg & PSP_CMDRESP_RESP)
+ return 0;
+
+ udelay(10);
+ }
+ return -ETIMEDOUT;
+ }
+
ret = wait_event_timeout(sev->int_queue,
sev->int_rcvd, timeout * HZ);
if (!ret)
@@ -1316,17 +1336,6 @@ static int __sev_platform_shutdown_locked(int *error)
return ret;
}

-static int sev_platform_shutdown(int *error)
-{
- int rc;
-
- mutex_lock(&sev_cmd_mutex);
- rc = __sev_platform_shutdown_locked(NULL);
- mutex_unlock(&sev_cmd_mutex);
-
- return rc;
-}
-
static int sev_get_platform_state(int *state, int *error)
{
struct sev_user_data_status data;
@@ -1602,7 +1611,7 @@ static int sev_update_firmware(struct device *dev)
return ret;
}

-static int __sev_snp_shutdown_locked(int *error)
+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;
@@ -1615,7 +1624,16 @@ static int __sev_snp_shutdown_locked(int *error)
data.len = sizeof(data);
data.iommu_snp_shutdown = 1;

- wbinvd_on_all_cpus();
+ /*
+ * If invoked during panic handling, local interrupts are disabled
+ * and all CPUs are stopped, so wbinvd_on_all_cpus() can't be called.
+ * In that case, a wbinvd() is done on remote CPUs via the NMI
+ * callback, so only a local wbinvd() is needed here.
+ */
+ if (!panic)
+ wbinvd_on_all_cpus();
+ else
+ wbinvd();

ret = __sev_do_cmd_locked(SEV_CMD_SNP_SHUTDOWN_EX, &data, error);
/* SHUTDOWN may require DF_FLUSH */
@@ -1659,17 +1677,6 @@ static int __sev_snp_shutdown_locked(int *error)
return ret;
}

-static int sev_snp_shutdown(int *error)
-{
- int rc;
-
- mutex_lock(&sev_cmd_mutex);
- rc = __sev_snp_shutdown_locked(error);
- mutex_unlock(&sev_cmd_mutex);
-
- return rc;
-}
-
static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp, bool writable)
{
struct sev_device *sev = psp_master->sev_data;
@@ -2117,19 +2124,28 @@ int sev_dev_init(struct psp_device *psp)
return ret;
}

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

- sev_platform_shutdown(NULL);
+ __sev_platform_shutdown_locked(NULL);

if (sev_es_tmr) {
- /* The TMR area was encrypted, flush it from the cache */
- wbinvd_on_all_cpus();
+ /*
+ * 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, and done for this CPU later during
+ * SNP shutdown, so wbinvd_on_all_cpus() can be skipped.
+ */
+ if (!panic)
+ wbinvd_on_all_cpus();

__snp_free_firmware_pages(virt_to_page(sev_es_tmr),
get_order(sev_es_tmr_size),
- false);
+ true);
sev_es_tmr = NULL;
}

@@ -2145,7 +2161,14 @@ static void sev_firmware_shutdown(struct sev_device *sev)
snp_range_list = NULL;
}

- sev_snp_shutdown(&error);
+ __sev_snp_shutdown_locked(&error, panic);
+}
+
+static void sev_firmware_shutdown(struct sev_device *sev)
+{
+ mutex_lock(&sev_cmd_mutex);
+ __sev_firmware_shutdown(sev, false);
+ mutex_unlock(&sev_cmd_mutex);
}

void sev_dev_destroy(struct psp_device *psp)
@@ -2163,6 +2186,29 @@ void sev_dev_destroy(struct psp_device *psp)
psp_clear_sev_irq_handler(psp);
}

+static int snp_shutdown_on_panic(struct notifier_block *nb,
+ unsigned long reason, void *arg)
+{
+ struct sev_device *sev = psp_master->sev_data;
+
+ /*
+ * If sev_cmd_mutex is already acquired, then it's likely
+ * another PSP command is in flight and issuing a shutdown
+ * would fail in unexpected ways. Rather than create even
+ * more confusion during a panic, just bail out here.
+ */
+ if (mutex_is_locked(&sev_cmd_mutex))
+ return NOTIFY_DONE;
+
+ __sev_firmware_shutdown(sev, true);
+
+ return NOTIFY_DONE;
+}
+
+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,
void *data, int *error)
{
@@ -2200,6 +2246,8 @@ void sev_pci_init(void)
dev_info(sev->dev, "SEV%s API:%d.%d build:%d\n", sev->snp_initialized ?
"-SNP" : "", sev->api_major, sev->api_minor, sev->build);

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

err:
@@ -2214,4 +2262,7 @@ void sev_pci_exit(void)
return;

sev_firmware_shutdown(sev);
+
+ atomic_notifier_chain_unregister(&panic_notifier_list,
+ &snp_panic_notifier);
}
--
2.25.1