Re: [RFC 0/9] Linear Address Masking enabling

[H.J. Lu]

On Tue, Sep 21, 2021 at 9:52 AM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
> On Sun, 7 Feb 2021 at 15:11, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
> >
> > On Sun, Feb 07, 2021 at 09:24:23AM +0100, Dmitry Vyukov wrote:
> > > On Fri, Feb 5, 2021 at 4:16 PM Kirill A. Shutemov
> > > <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> > > >
> > > > Linear Address Masking[1] (LAM) modifies the checking that is applied to
> > > > 64-bit linear addresses, allowing software to use of the untranslated
> > > > address bits for metadata.
> > > >
> > > > The patchset brings support for LAM for userspace addresses.
> > > >
> > > > The most sensitive part of enabling is change in tlb.c, where CR3 flags
> > > > get set. Please take a look that what I'm doing makes sense.
> > > >
> > > > The patchset is RFC quality and the code requires more testing before it
> > > > can be applied.
> > > >
> > > > The userspace API is not finalized yet. The patchset extends API used by
> > > > ARM64: PR_GET/SET_TAGGED_ADDR_CTRL. The API is adjusted to not imply ARM
> > > > TBI: it now allows to request a number of bits of metadata needed and
> > > > report where these bits are located in the address.
> > > >
> > > > There's an alternative proposal[2] for the API based on Intel CET
> > > > interface. Please let us know if you prefer one over another.
> > > >
> > > > The feature competes for bits with 5-level paging: LAM_U48 makes it
> > > > impossible to map anything about 47-bits. The patchset made these
> > > > capability mutually exclusive: whatever used first wins. LAM_U57 can be
> > > > combined with mappings above 47-bits.
> > > >
> > > > I include QEMU patch in case if somebody wants to play with the feature.
> > >
> > > Exciting! Do you plan to send the QEMU patch to QEMU?
> >
> > Sure. After more testing, once I'm sure it's conforming to the hardware.
>
> A follow up after H.J.'s LPC talk:
> https://linuxplumbersconf.org/event/11/contributions/1010/
> (also +Carlos)
>
> As far as I understood, this kernel series depends on the Intel CET patches.
>
> Where are these compiler-rt patches that block gcc support?

Hi Xiang,

Please share your compiler-rt changes for LAM.

-- 
H.J.