From: Moe Mahhouk wait_for_quote_completion() sleeps for a full second before it first checks whether the VMM has completed a GetQuote request, and then rechecks once per second. Every Quote request therefore takes at least one second, however quickly the host answers. With a local Quote Generation Service the VMM completes the request in a few milliseconds. On an Emerald Rapids host (KVM, QEMU 11.1, Intel QGS), back-to-back Quote requests through configfs-tsm took 1021-1024 ms each; with this change they take 6-12 ms at HZ=250. Since quote_lock serializes requests, the one-second floor also caps a TD at about one Quote per second, which hurts users that bind a fresh Quote to every connection, such as attested TLS. Poll with an exponential backoff instead: sleep 1 ms first and double the interval up to 100 ms, so that a fast Quote is noticed within a few milliseconds while a slow one costs at most ten wakeups per second. The sleep stays interruptible, and the timeout becomes a deadline in jiffies. Signed-off-by: Moe Mahhouk --- drivers/virt/coco/tdx-guest/tdx-guest.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/drivers/virt/coco/tdx-guest/tdx-guest.c b/drivers/virt/coco/tdx-guest/tdx-guest.c index a5a53174f9d9..000fff4ef6f5 100644 --- a/drivers/virt/coco/tdx-guest/tdx-guest.c +++ b/drivers/virt/coco/tdx-guest/tdx-guest.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #include #include @@ -271,18 +272,24 @@ static struct tdx_quote_buf *alloc_quote_buf(void) */ static int wait_for_quote_completion(struct tdx_quote_buf *buf, u32 timeout) { - int i = 0; + unsigned long deadline = jiffies + secs_to_jiffies(timeout); + unsigned int sleep_ms = 1; /* - * Quote requests usually take a few seconds to complete, so waking up - * once per second to recheck the status is fine for this use case. + * A local Quote Generation Service usually completes the request + * within a few milliseconds. Poll with an exponential backoff, from + * 1 ms up to 100 ms, so that a fast Quote is noticed promptly while + * a slow one costs at most ten wakeups per second. */ - while (buf->status == GET_QUOTE_IN_FLIGHT && i++ < timeout) { - if (msleep_interruptible(MSEC_PER_SEC)) + while (READ_ONCE(buf->status) == GET_QUOTE_IN_FLIGHT) { + if (time_after(jiffies, deadline)) + return -ETIMEDOUT; + if (msleep_interruptible(sleep_ms)) return -EINTR; + sleep_ms = min(2 * sleep_ms, 100U); } - return (buf->status == GET_QUOTE_IN_FLIGHT) ? -ETIMEDOUT : 0; + return 0; } static int tdx_report_new_locked(struct tsm_report *report) -- 2.34.1