From: Dave Hansen <dave.hansen@intel.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-kernel@vger.kernel.org
Cc: x86@kernel.org, jannh@google.com, riel@surriel.com,
mingo@redhat.com, bp@suse.de, Jason@zx2c4.com, luto@kernel.org,
tglx@linutronix.de, rkrcmar@redhat.com, mingo@kernel.org,
hpa@zytor.com, kvm@vger.kernel.org, pbonzini@redhat.com,
kurt.kanzenbach@linutronix.de
Subject: Re: [RFC PATCH] x86/fpu: Don't unconditionally add XFEATURE_MASK_FPSSE on sigentry
Date: Thu, 25 Apr 2019 14:13:05 -0700 [thread overview]
Message-ID: <cbb4c3de-1e12-c325-fa7f-40bc63c495e7@intel.com> (raw)
In-Reply-To: <20190425173545.sogxyptbaqvoofm6@linutronix.de>
On 4/25/19 10:35 AM, Sebastian Andrzej Siewior wrote:
> This commit reverts commit 04944b793e18e ("x86: xsave: set FP, SSE bits
> in the xsave header in the user sigcontext"). The commit claims that it
> is required for legacy applications but fails to explain why this is
> needed and it is not obvious to me why the application would require the
> FP/SSE state in the signal handler.
Any software that understands XSAVE is OK. I think the legacy software
would be that which groks 'fxregs_state, and FXSAVE/FXRSTOR but does not
comprehend XSAVE/XRSTOR. *That* software might change fxregs_state in
the signal frame, but the lack of XFEATURE_MASK_FPSSE in xfeatures would
prevent XRSTOR from restoring it.
That's just a guess, though.
If we care, I think we should just use XSAVE instead of XSAVEOPT and
trying to reconstruct the init state in software.
next prev parent reply other threads:[~2019-04-25 21:13 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-25 17:35 [RFC PATCH] x86/fpu: Don't unconditionally add XFEATURE_MASK_FPSSE on sigentry Sebastian Andrzej Siewior
2019-04-25 21:13 ` Dave Hansen [this message]
2019-04-26 7:26 ` Sebastian Andrzej Siewior
2019-04-26 16:33 ` Dave Hansen
2019-04-26 16:50 ` Sebastian Andrzej Siewior
2019-04-26 19:04 ` Dave Hansen
2019-04-26 20:05 ` Sebastian Andrzej Siewior
2019-04-26 20:44 ` Dave Hansen
2019-04-29 16:39 ` [PATCH] x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails Sebastian Andrzej Siewior
2019-04-29 18:52 ` [tip:x86/fpu] " tip-bot for Sebastian Andrzej Siewior
2019-04-30 14:20 ` Dave Hansen
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