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identity=mailfrom; envelope-from=""; helo=NAM12-DM6-obe.outbound.protection.outlook.com; client-ip=40.107.243.81 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616694908-810548 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 25, 2021 at 06:51:26PM +0100, Thomas Hellstr=C3=B6m (Intel) w= rote: >=20 > On 3/24/21 9:25 PM, Dave Hansen wrote: > > On 3/24/21 1:22 PM, Thomas Hellstr=C3=B6m (Intel) wrote: > > > > We also have not been careful at *all* about how _PAGE_BIT_SOFTW*= are > > > > used.=C2=A0 It's quite possible we can encode another use even in= the > > > > existing bits. > > > >=20 > > > > Personally, I'd just try: > > > >=20 > > > > #define _PAGE_BIT_SOFTW5=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= 57=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* available for programmer */ > > > >=20 > > > OK, I'll follow your advise here. FWIW I grepped for SW1 and it see= ms > > > used in a selftest, but only for PTEs AFAICT. > > >=20 > > > Oh, and we don't care about 32-bit much anymore? > > On x86, we have 64-bit PTEs when running 32-bit kernels if PAE is > > enabled. IOW, we can handle the majority of 32-bit CPUs out there. > >=20 > > But, yeah, we don't care about 32-bit. :) >=20 > Hmm, >=20 > Actually it makes some sense to use SW1, to make it end up in the same = dword > as the PSE bit, as from what I can tell, reading of a 64-bit pmd_t on 3= 2-bit > PAE is not atomic, so in theory a huge pmd could be modified while read= ing > the pmd_t making the dwords inconsistent.... How does that work with fa= st > gup anyway? It loops to get an atomic 64 bit value if the arch can't provide an atomic 64 bit load Jason