From: Ingo Molnar <mingo@kernel.org>
To: xlpang@redhat.com
Cc: Yinghai Lu <yinghai@kernel.org>,
x86@kernel.org, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org, Borislav Petkov <bp@alien8.de>,
Eric Biederman <ebiederm@xmission.com>,
Andy Lutomirski <luto@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
akpm@linux-foundation.org, Dave Young <dyoung@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v3 2/2] x86_64/kexec: Use PUD level 1GB page for identity mapping if available
Date: Fri, 5 May 2017 11:20:46 +0200 [thread overview]
Message-ID: <20170505092046.2qu72pdherfxjmec@gmail.com> (raw)
In-Reply-To: <590C2A96.3090106@redhat.com>
* Xunlei Pang <xpang@redhat.com> wrote:
> On 05/05/2017 at 02:52 PM, Ingo Molnar wrote:
> > * Xunlei Pang <xlpang@redhat.com> wrote:
> >
> >> @@ -122,6 +122,10 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
> >>
> >> level4p = (pgd_t *)__va(start_pgtable);
> >> clear_page(level4p);
> >> +
> >> + if (direct_gbpages)
> >> + info.direct_gbpages = true;
> > No, this should be keyed off the CPU feature (X86_FEATURE_GBPAGES) automatically,
> > not set blindly! AFAICS this patch will crash kexec on any CPU that does not
> > support gbpages.
>
> It should be fine, probe_page_size_mask() already takes care of this:
> if (direct_gbpages && boot_cpu_has(X86_FEATURE_GBPAGES)) {
> printk(KERN_INFO "Using GB pages for direct mapping\n");
> page_size_mask |= 1 << PG_LEVEL_1G;
> } else {
> direct_gbpages = 0;
> }
>
> So if X86_FEATURE_GBPAGES is not supported, direct_gbpages will be set to 0.
So why is the introduction of the info.direct_gbpages flag necessary? AFAICS it
just duplicates the kernel's direct_gbpages flag. One outcome is that hibernation
won't use gbpages, which is silly.
Thanks,
Ingo
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WARNING: multiple messages have this Message-ID (diff)
From: Ingo Molnar <mingo@kernel.org>
To: xlpang@redhat.com
Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
akpm@linux-foundation.org, Eric Biederman <ebiederm@xmission.com>,
Dave Young <dyoung@redhat.com>,
x86@kernel.org, Borislav Petkov <bp@alien8.de>,
Thomas Gleixner <tglx@linutronix.de>,
Yinghai Lu <yinghai@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH v3 2/2] x86_64/kexec: Use PUD level 1GB page for identity mapping if available
Date: Fri, 5 May 2017 11:20:46 +0200 [thread overview]
Message-ID: <20170505092046.2qu72pdherfxjmec@gmail.com> (raw)
In-Reply-To: <590C2A96.3090106@redhat.com>
* Xunlei Pang <xpang@redhat.com> wrote:
> On 05/05/2017 at 02:52 PM, Ingo Molnar wrote:
> > * Xunlei Pang <xlpang@redhat.com> wrote:
> >
> >> @@ -122,6 +122,10 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
> >>
> >> level4p = (pgd_t *)__va(start_pgtable);
> >> clear_page(level4p);
> >> +
> >> + if (direct_gbpages)
> >> + info.direct_gbpages = true;
> > No, this should be keyed off the CPU feature (X86_FEATURE_GBPAGES) automatically,
> > not set blindly! AFAICS this patch will crash kexec on any CPU that does not
> > support gbpages.
>
> It should be fine, probe_page_size_mask() already takes care of this:
> if (direct_gbpages && boot_cpu_has(X86_FEATURE_GBPAGES)) {
> printk(KERN_INFO "Using GB pages for direct mapping\n");
> page_size_mask |= 1 << PG_LEVEL_1G;
> } else {
> direct_gbpages = 0;
> }
>
> So if X86_FEATURE_GBPAGES is not supported, direct_gbpages will be set to 0.
So why is the introduction of the info.direct_gbpages flag necessary? AFAICS it
just duplicates the kernel's direct_gbpages flag. One outcome is that hibernation
won't use gbpages, which is silly.
Thanks,
Ingo
next prev parent reply other threads:[~2017-05-05 9:21 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-04 1:42 [PATCH v3 1/2] x86/mm/ident_map: Add PUD level 1GB page support Xunlei Pang
2017-05-04 1:42 ` Xunlei Pang
2017-05-04 1:42 ` [PATCH v3 2/2] x86_64/kexec: Use PUD level 1GB page for identity mapping if available Xunlei Pang
2017-05-04 1:42 ` Xunlei Pang
2017-05-05 6:52 ` Ingo Molnar
2017-05-05 6:52 ` Ingo Molnar
2017-05-05 7:32 ` Xunlei Pang
2017-05-05 7:32 ` Xunlei Pang
2017-05-05 9:20 ` Ingo Molnar [this message]
2017-05-05 9:20 ` Ingo Molnar
2017-05-05 10:50 ` Xunlei Pang
2017-05-05 10:50 ` Xunlei Pang
2017-05-08 6:29 ` Ingo Molnar
2017-05-08 6:29 ` Ingo Molnar
2017-05-08 7:24 ` Xunlei Pang
2017-05-08 7:24 ` Xunlei Pang
2017-05-08 8:01 ` [tip:x86/urgent] x86/kexec/64: Use gbpages for identity mappings " tip-bot for Xunlei Pang
2017-05-08 8:01 ` [tip:x86/urgent] x86/mm: Add support for gbpages to kernel_ident_mapping_init() tip-bot for Xunlei Pang
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