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Re: [PATCH v4 2/6] introduce UFFD-WP low-level interface helpers

From: Andrey Gruzdev
Subject: Re: [PATCH v4 2/6] introduce UFFD-WP low-level interface helpers
Date: Mon, 30 Nov 2020 21:41:44 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0

On 30.11.2020 18:34, Peter Xu wrote:
On Sun, Nov 29, 2020 at 11:12:10PM +0300, Andrey Gruzdev wrote:
+void ram_write_tracking_stop(void)
+    RAMState *rs = ram_state;
+    RAMBlock *bs;
+    assert(rs->uffdio_fd >= 0);

Maybe too harsh - we can return if it's invalid.

Meanwhile, better rcu_read_lock(), as well?

Yep, RCU lock, I'll add. Why too harsh? Just a debug assertion.

I was afraid some special path could trigger ram_write_tracking_stop() being
called before ram_write_tracking_start(), then vm could crash.  If we can
guarantee that not happening, then it's also ok with assert().


It can't really happen, but I agree that assert() is a bit excessive here.

+ * uffd_poll_events: poll UFFD file descriptor for read
+ *
+ * Returns true if events are available for read, false otherwise
+ *
+ * @uffd: UFFD file descriptor
+ * @tmo: timeout in milliseconds, 0 for non-blocking operation,
+ *       negative value for infinite wait
+ */
+bool uffd_poll_events(int uffd, int tmo)

Shall we spell "tmo" out?
In the comment? I think it's ok.

I'd suggest to spell it out everywhere, especially in the codes.  But feel free
to take your own preference.  Thanks,


Andrey Gruzdev, Principal Engineer
Virtuozzo GmbH  +7-903-247-6397

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