From: Linus Torvalds <torvalds@linux-foundation.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Christian Kujau <lists@nerdbynature.de>,
Juergen Gross <jgross@suse.com>,
Michael Kelley <mikelley@microsoft.com>,
linux-kernel@vger.kernel.org,
Greg KH <gregkh@linuxfoundation.org>,
Linux regressions mailing list <regressions@lists.linux.dev>
Subject: Re: External USB disks not recognized with v6.1.8 when using Xen
Date: Sun, 5 Feb 2023 12:21:42 -0800 [thread overview]
Message-ID: <CAHk-=wgC_MEFnnzUGN4q9pmhxV+eFV1Oo=W2j1J69YhJF5EDtw@mail.gmail.com> (raw)
In-Reply-To: <Y9+tDmLAlqg37TS+@zn.tnic>
On Sun, Feb 5, 2023 at 5:20 AM Borislav Petkov <bp@alien8.de> wrote:
>
> @@ -53,7 +53,8 @@ static inline u8 mtrr_type_lookup(u64 addr,
> /*
> * Return no-MTRRs:
> */
> - return MTRR_TYPE_INVALID;
> + *uniform = 1;
> + return MTRR_TYPE_UNCACHABLE;
So this is the one I'd almost leave alone.
Because this is not a "there are no MTRR's" situation, this is a "I
haven't enabled CONFIG_MTRR, so I don't _know_ if there are any MTRR's
or not.
And returning MTRR_TYPE_UNCACHABLE will then disable things like
largepages etc, so this change would effectively mean that if
CONFIG_MTRR is off, it would turn off hugepage support too.
But maybe that was the only thing that cared, and we have:
> @@ -721,8 +721,9 @@ int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
> u8 mtrr, uniform;
>
> mtrr = mtrr_type_lookup(addr, addr + PUD_SIZE, &uniform);
> - if ((mtrr != MTRR_TYPE_INVALID) && (!uniform) &&
> - (mtrr != MTRR_TYPE_WRBACK))
> + if (mtrr != MTRR_TYPE_UNCACHABLE &&
> + mtrr != MTRR_TYPE_WRBACK &&
> + !uniform)
> return 0;
Here you make up for it, but I don't actually understand why these
checks exist at all.
I *think* that what the check should do is just check for uniformity.
Why would the largepage code otherwise care?
Other MTRR types are explicitly fine, and I think things like the X
server might even want to do write-combining with large pages etc.
So I think the hugepage code should only do
if (!uniform)
return 0;
or there should be some explanation for why those types are special?
>> @@ -748,8 +749,9 @@ int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot)
> u8 mtrr, uniform;
>
> mtrr = mtrr_type_lookup(addr, addr + PMD_SIZE, &uniform);
> - if ((mtrr != MTRR_TYPE_INVALID) && (!uniform) &&
> - (mtrr != MTRR_TYPE_WRBACK)) {
> + if (mtrr != MTRR_TYPE_UNCACHABLE &&
> + mtrr != MTRR_TYPE_WRBACK &&
> + !uniform) {
Same here.
Again, I *think* that the reason it used to do that "check two types"
thing is simply because "uniform" wasn't set correctly.
But I don't know.
Linus
next prev parent reply other threads:[~2023-02-05 20:22 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-30 3:46 External USB disks not recognized with v6.1.8 when using Xen Christian Kujau
2023-01-30 5:17 ` Greg KH
2023-01-30 12:01 ` Linux kernel regression tracking (#adding)
2023-01-31 22:50 ` Christian Kujau
2023-02-01 8:14 ` Juergen Gross
2023-02-01 9:37 ` Christian Kujau
2023-02-02 11:38 ` Christian Kujau
2023-02-02 20:24 ` Linus Torvalds
2023-02-03 16:50 ` Christian Kujau
2023-02-03 17:29 ` Christian Kujau
2023-02-05 13:20 ` Borislav Petkov
2023-02-05 17:17 ` Christian Kujau
2023-02-05 20:21 ` Linus Torvalds [this message]
2023-02-06 6:33 ` Juergen Gross
2023-02-06 9:54 ` Juergen Gross
2023-02-06 9:43 ` Borislav Petkov
2023-02-05 10:40 ` Linux kernel regression tracking (#update)
2023-02-14 9:35 ` [tip: x86/urgent] x86/mtrr: Revert 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case") tip-bot2 for Juergen Gross
2023-02-18 9:47 ` Christian Kujau
2023-02-18 9:59 ` Borislav Petkov
2023-05-08 13:41 ` [tip: x86/cleanups] Documentation/process: Explain when tip branches get merged into mainline tip-bot2 for Christian Kujau
2023-05-15 15:28 ` tip-bot2 for Christian Kujau
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