From: Ahmed Karaman <ahmedkhaledkaraman@gmail.com>
To: Richard Henderson <richard.henderson@linaro.org>,
QEMU Developers <qemu-devel@nongnu.org>,
rth@twiddle.net, ysato@users.sourceforge.jp
Cc: "Aleksandar Markovic" <aleksandar.qemu.devel@gmail.com>,
"Alex Bennée" <alex.bennee@linaro.org>,
stefanha@redhat.com
Subject: Re: [PATCH 0/2] Update use_goto_tb() in hppa and rx targets
Date: Thu, 21 May 2020 13:32:27 +0200 [thread overview]
Message-ID: <CALTWKrVGqVb1mjsaoxYm4Y1iQoXYwz7ToC7T6r2EDPp-_LO=LQ@mail.gmail.com> (raw)
In-Reply-To: <a0f3967f-e125-d888-bc6d-44414edbfd5b@linaro.org>
On Tue, May 19, 2020 at 8:01 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 5/19/20 9:21 AM, Ahmed Karaman wrote:
> > The issue arose because the page crossings check in use_goto_tb()
> > function is required only in the system mode. Checking it in both
> > modes causes an unnecessary overhead in the user mode.
>
> It is not only required in system mode.
>
> You can see failures in user-mode if you modify executable pages, or
> change their permissions with mmap. Such as if the guest program
> contains a JIT.
>
>
> r~
Hi Mr. Richard,
I've checked how the use_goto_tb() function is implemented in other
targets, and it appears that they do the page crossings check in the
system mode only.
Below is an example from the arm64 target:
-----------------------------------------------------------------------
static inline bool use_goto_tb(DisasContext *s, int n, uint64_t dest)
{
/* No direct tb linking with singlestep (either QEMU's or the ARM
* debug architecture kind) or deterministic io
*/
if (s->base.singlestep_enabled || s->ss_active ||
(tb_cflags(s->base.tb) & CF_LAST_IO)) {
return false;
}
#ifndef CONFIG_USER_ONLY
/* Only link tbs from inside the same guest page */
if ((s->base.tb->pc & TARGET_PAGE_MASK)!=(dest & TARGET_PAGE_MASK)) {
return false;
}
#endif
return true;
}
-----------------------------------------------------------------------
Please let me know what you think. Does this mean that there is a bug
in this function for the other targets?
That we have to do the page crossings check in both modes to avoid the
user-mode failures that you have mentioned above?
Regards,
Ahmed Karaman
next prev parent reply other threads:[~2020-05-21 11:33 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-19 16:21 [PATCH 0/2] Update use_goto_tb() in hppa and rx targets Ahmed Karaman
2020-05-19 16:21 ` [PATCH 1/2] target/hppa: Check page crossings in use_goto_tb() only in system mode Ahmed Karaman
2020-05-19 16:21 ` [PATCH 2/2] target/rx: Check for page crossings in use_goto_tb() Ahmed Karaman
2020-05-19 18:01 ` [PATCH 0/2] Update use_goto_tb() in hppa and rx targets Richard Henderson
2020-05-19 18:38 ` Alex Bennée
2020-05-19 18:51 ` Richard Henderson
2020-05-21 11:32 ` Ahmed Karaman [this message]
2020-05-22 3:12 ` Richard Henderson
2020-05-25 18:39 ` Aleksandar Markovic
2020-05-26 14:14 ` Aleksandar Markovic
2020-05-26 16:08 ` Ahmed Karaman
2020-05-26 16:29 ` Aleksandar Markovic
2020-05-26 16:45 ` Aleksandar Markovic
2020-05-26 17:38 ` Aleksandar Markovic
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CALTWKrVGqVb1mjsaoxYm4Y1iQoXYwz7ToC7T6r2EDPp-_LO=LQ@mail.gmail.com' \
--to=ahmedkhaledkaraman@gmail.com \
--cc=aleksandar.qemu.devel@gmail.com \
--cc=alex.bennee@linaro.org \
--cc=qemu-devel@nongnu.org \
--cc=richard.henderson@linaro.org \
--cc=rth@twiddle.net \
--cc=stefanha@redhat.com \
--cc=ysato@users.sourceforge.jp \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).