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Date: Fri, 26 Jan 2024 16:11:13 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Nikunj A Dadhania <nikunj@....com>, linux-kernel@...r.kernel.org,
x86@...nel.org, kvm@...r.kernel.org
Cc: bp@...en8.de, mingo@...hat.com, tglx@...utronix.de,
dave.hansen@...ux.intel.com, dionnaglaze@...gle.com, pgonda@...gle.com,
seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v7 06/16] virt: sev-guest: Move SNP Guest command mutex
On 12/20/23 09:13, Nikunj A Dadhania wrote:
> SNP command mutex is used to serialize the shared buffer access, command
> handling and message sequence number races. Move the SNP guest command
> mutex out of the sev guest driver and provide accessors to sev-guest
> driver. Remove multiple lockdep check in sev-guest driver, next patch adds
> a single lockdep check in snp_send_guest_request().
>
> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
> ---
> arch/x86/include/asm/sev-guest.h | 3 +++
> arch/x86/kernel/sev.c | 21 +++++++++++++++++++++
> drivers/virt/coco/sev-guest/sev-guest.c | 23 +++++++----------------
> 3 files changed, 31 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/include/asm/sev-guest.h b/arch/x86/include/asm/sev-guest.h
> index 27cc15ad6131..2f3cceb88396 100644
> --- a/arch/x86/include/asm/sev-guest.h
> +++ b/arch/x86/include/asm/sev-guest.h
> @@ -81,4 +81,7 @@ struct snp_guest_req {
>
> int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_data *input,
> struct snp_guest_request_ioctl *rio);
> +void snp_guest_cmd_lock(void);
> +void snp_guest_cmd_unlock(void);
> +
> #endif /* __VIRT_SEVGUEST_H__ */
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 6aa0bdf8a7a0..191193924b22 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -941,6 +941,21 @@ static void snp_cleanup_vmsa(struct sev_es_save_area *vmsa)
> free_page((unsigned long)vmsa);
> }
>
> +/* SNP Guest command mutex to serialize the shared buffer access and command handling. */
> +static struct mutex snp_guest_cmd_mutex;
You should probably use:
static DEFINE_MUTEX(snp_guest_cmd_mutex);
That way you can avoid the initialization in snp_init_platform_device().
With that:
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> +
> +void snp_guest_cmd_lock(void)
> +{
> + mutex_lock(&snp_guest_cmd_mutex);
> +}
> +EXPORT_SYMBOL_GPL(snp_guest_cmd_lock);
> +
> +void snp_guest_cmd_unlock(void)
> +{
> + mutex_unlock(&snp_guest_cmd_mutex);
> +}
> +EXPORT_SYMBOL_GPL(snp_guest_cmd_unlock);
> +
> static int wakeup_cpu_via_vmgexit(u32 apic_id, unsigned long start_ip)
> {
> struct sev_es_save_area *cur_vmsa, *vmsa;
> @@ -2240,6 +2255,12 @@ static int __init snp_init_platform_device(void)
> return -ENODEV;
> }
>
> + /*
> + * Initialize snp command mutex that is used to serialize the shared
> + * buffer access and use of the vmpck and message sequence number
> + */
> + mutex_init(&snp_guest_cmd_mutex);
> +
> data.secrets_gpa = secrets_pa;
> if (platform_device_add_data(&sev_guest_device, &data, sizeof(data)))
> return -ENODEV;
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index 9c0ff69a16da..bd30a9ff82c1 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -63,9 +63,6 @@ static u32 vmpck_id;
> module_param(vmpck_id, uint, 0444);
> MODULE_PARM_DESC(vmpck_id, "The VMPCK ID to use when communicating with the PSP.");
>
> -/* Mutex to serialize the shared buffer access and command handling. */
> -static DEFINE_MUTEX(snp_cmd_mutex);
> -
> static inline u8 *snp_get_vmpck(struct snp_guest_dev *snp_dev)
> {
> return snp_dev->layout->vmpck0 + snp_dev->vmpck_id * VMPCK_KEY_LEN;
> @@ -115,8 +112,6 @@ static inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
> u32 *os_area_msg_seqno = snp_get_os_area_msg_seqno(snp_dev);
> u64 count;
>
> - lockdep_assert_held(&snp_cmd_mutex);
> -
> /* Read the current message sequence counter from secrets pages */
> count = *os_area_msg_seqno;
>
> @@ -409,8 +404,6 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
> struct snp_report_resp *resp;
> int rc, resp_len;
>
> - lockdep_assert_held(&snp_cmd_mutex);
> -
> if (!arg->req_data || !arg->resp_data)
> return -EINVAL;
>
> @@ -457,8 +450,6 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
> /* Response data is 64 bytes and max authsize for GCM is 16 bytes. */
> u8 buf[64 + 16];
>
> - lockdep_assert_held(&snp_cmd_mutex);
> -
> if (!arg->req_data || !arg->resp_data)
> return -EINVAL;
>
> @@ -507,8 +498,6 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
> sockptr_t certs_address;
> int ret, resp_len;
>
> - lockdep_assert_held(&snp_cmd_mutex);
> -
> if (sockptr_is_null(io->req_data) || sockptr_is_null(io->resp_data))
> return -EINVAL;
>
> @@ -604,12 +593,12 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
> if (!input.msg_version)
> return -EINVAL;
>
> - mutex_lock(&snp_cmd_mutex);
> + snp_guest_cmd_lock();
>
> /* Check if the VMPCK is not empty */
> if (snp_is_vmpck_empty(snp_dev)) {
> dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
> - mutex_unlock(&snp_cmd_mutex);
> + snp_guest_cmd_unlock();
> return -ENOTTY;
> }
>
> @@ -634,7 +623,7 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
> break;
> }
>
> - mutex_unlock(&snp_cmd_mutex);
> + snp_guest_cmd_unlock();
>
> if (input.exitinfo2 && copy_to_user(argp, &input, sizeof(input)))
> return -EFAULT;
> @@ -724,14 +713,14 @@ static int sev_report_new(struct tsm_report *report, void *data)
> if (!buf)
> return -ENOMEM;
>
> - guard(mutex)(&snp_cmd_mutex);
> -
> /* Check if the VMPCK is not empty */
> if (snp_is_vmpck_empty(snp_dev)) {
> dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
> return -ENOTTY;
> }
>
> + snp_guest_cmd_lock();
> +
> cert_table = buf + report_size;
> struct snp_ext_report_req ext_req = {
> .data = { .vmpl = desc->privlevel },
> @@ -752,6 +741,8 @@ static int sev_report_new(struct tsm_report *report, void *data)
> };
>
> ret = get_ext_report(snp_dev, &input, &io);
> + snp_guest_cmd_unlock();
> +
> if (ret)
> return ret;
>
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