linux-kernel - Re: [PATCH 08/15] riscv: provide native clint access for M-mode

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190821004241.GA20250@lst.de>
Date:   Wed, 21 Aug 2019 02:42:41 +0200
From:   "hch@....de" <hch@....de>
To:     Atish Patra <Atish.Patra@....com>
Cc:     "hch@....de" <hch@....de>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        Damien Le Moal <Damien.LeMoal@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/15] riscv: provide native clint access for M-mode

On Wed, Aug 21, 2019 at 12:24:31AM +0000, Atish Patra wrote:
> > +static inline void clint_set_timer(unsigned long delta)
> > +{
> > +	writeq_relaxed(clint_read_timer() + delta,
> > +		clint_time_cmp +
> > cpuid_to_hartid_map(smp_processor_id()));'
> 
> This is not compatible with 32 bit mode. IIRC, timecmp is a 64 bit on
> RV32 as well. Here is the implementation in OpenSBI.

writeq alwasy writes 64-bit anyway, but the deltas is just 32-bit
per the Linux clocksource API.

> > +static inline cycles_t get_cycles(void)
> > +{
> > +#ifdef CONFIG_64BIT
> > +	return readq_relaxed(clint_time_val);
> > +#else
> > +	return readl_relaxed(clint_time_val);
> > +#endif
> 
> Same comment as above. Both RV32 & RV64 bit have 64 bit have 64 bit
> precission for timer val. You have to read 32 bits at a time and "or"
> them to get 64 bit value. Here is the implementation from OpenSBI

But the Linux API is only going to read 32-bits of that, same as
for the rdtime pseudo-instruction used by the current SBI-based code.

Note that I've reworked this area a bit for v4, which I'm going to
send out soon, including cleanups to the existing code to make a few
of these things more obvious:

http://git.infradead.org/users/hch/riscv.git/shortlog/refs/heads/riscv-nommu.4