From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>,
Jonathan Corbet <corbet@lwn.net>,
Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
tony.luck@intel.com, ak@linux.intel.com,
tim.c.chen@linux.intel.com, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, kvm@vger.kernel.org,
Alyssa Milburn <alyssa.milburn@linux.intel.com>,
Daniel Sneddon <daniel.sneddon@linux.intel.com>,
antonio.gomez.iglesias@linux.intel.com,
Alyssa Milburn <alyssa.milburn@intel.com>
Subject: Re: [RESEND][PATCH 1/6] x86/bugs: Add asm helpers for executing VERW
Date: Mon, 23 Oct 2023 12:09:49 -0700 [thread overview]
Message-ID: <20231023190949.2gdrqisype5metpj@desk> (raw)
In-Reply-To: <20231023180806.udbnt4nx3r2bdyi3@treble>
On Mon, Oct 23, 2023 at 11:08:06AM -0700, Josh Poimboeuf wrote:
> On Fri, Oct 20, 2023 at 07:21:34PM -0700, Pawan Gupta wrote:
> > On Sat, Oct 21, 2023 at 02:33:47AM +0100, Andrew Cooper wrote:
> > > On 21/10/2023 2:18 am, Pawan Gupta wrote:
> > > > On Sat, Oct 21, 2023 at 12:55:45AM +0100, Andrew Cooper wrote:
> > > >> Also it avoids playing games with hiding data inside an instruction.
> > > >> It's a neat trick, but the neater trick is avoid it whenever possible.
> > > > Thanks for the pointers. I think verw in 32-bit mode won't be able to
> > > > address the operand outside of 4GB range.
> > >
> > > And? In a 32bit kernel, what lives outside of a 4G range?
> > >
> > > > Maybe this is fine or could it
> > > > be a problem addressing from e.g. KVM module?
> > >
> > > RIP-relative addressing is disp32. Which is the same as it is for
> > > direct calls.
> > >
> > > So if your module is far enough away for VERW to have issues, you've got
> > > far more basic problems to solve first.
> >
> > Sorry, I raised the wrong problem. In 64-bit mode, verww only has 32-bit
> > of relative addressing, so memory operand has to be within 4GB of
> > callsite. That could be a constraint.
>
> Even on x86-64, modules are mapped within 4GB of the kernel, so I don't
> think that's a concern.
You are correct, modules are indeed mapped within 4GB of the kernel. So
what Andrew suggested is feasible. Is that your preference?
next prev parent reply other threads:[~2023-10-23 19:10 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-20 20:44 [PATCH 0/6] Delay VERW Pawan Gupta
2023-10-20 20:44 ` [PATCH 1/6] x86/bugs: Add asm helpers for executing VERW Pawan Gupta
2023-10-20 23:13 ` Sean Christopherson
2023-10-21 1:00 ` Pawan Gupta
2023-10-20 23:55 ` [RESEND][PATCH " Andrew Cooper
2023-10-21 1:18 ` Pawan Gupta
2023-10-21 1:33 ` Andrew Cooper
2023-10-21 2:21 ` Pawan Gupta
2023-10-23 18:08 ` Josh Poimboeuf
2023-10-23 19:09 ` Pawan Gupta [this message]
2023-10-25 6:28 ` Pawan Gupta
2023-10-25 7:22 ` Peter Zijlstra
2023-10-25 7:52 ` Andrew Cooper
2023-10-25 8:02 ` Peter Zijlstra
2023-10-25 15:27 ` Pawan Gupta
[not found] ` <6439a094-23a6-4de3-aa41-bd033163e044@citrix.com>
2023-10-22 16:16 ` [PATCH " Peter Zijlstra
2023-10-20 20:45 ` [PATCH 2/6] x86/entry_64: Add VERW just before userspace transition Pawan Gupta
2023-10-23 18:22 ` Josh Poimboeuf
2023-10-23 19:13 ` Pawan Gupta
2023-10-23 19:17 ` Dave Hansen
2023-10-23 18:35 ` Josh Poimboeuf
2023-10-23 21:04 ` Pawan Gupta
2023-10-23 21:47 ` Josh Poimboeuf
2023-10-23 22:30 ` Pawan Gupta
2023-10-23 22:45 ` Dave Hansen
2023-10-24 0:00 ` Pawan Gupta
2023-10-20 20:45 ` [PATCH 3/6] x86/entry_32: " Pawan Gupta
2023-10-20 23:49 ` Andi Kleen
2023-10-21 1:28 ` Pawan Gupta
2023-10-20 20:45 ` [PATCH 4/6] x86/bugs: Use ALTERNATIVE() instead of mds_user_clear static key Pawan Gupta
2023-10-23 18:48 ` Josh Poimboeuf
2023-10-23 21:09 ` Pawan Gupta
2023-10-20 20:45 ` [PATCH 5/6] x86/bugs: Cleanup mds_user_clear Pawan Gupta
2023-10-23 8:51 ` Nikolay Borisov
2023-10-23 16:06 ` Pawan Gupta
2023-10-20 20:45 ` [PATCH 6/6] KVM: VMX: Move VERW closer to VMentry for MDS mitigation Pawan Gupta
2023-10-20 22:55 ` Sean Christopherson
2023-10-21 0:46 ` Pawan Gupta
2023-10-23 14:58 ` Sean Christopherson
2023-10-23 17:05 ` Pawan Gupta
2023-10-23 18:56 ` Josh Poimboeuf
2023-10-23 21:17 ` Pawan Gupta
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