From: Brijesh Singh <brijesh.singh@amd.com>
To: Borislav Petkov <bp@suse.de>
Cc: brijesh.singh@amd.com, linux-kernel@vger.kernel.org,
x86@kernel.org, linux-efi@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"H . Peter Anvin" <hpa@zytor.com>,
"Andy Lutomirski" <luto@kernel.org>,
"Tony Luck" <tony.luck@intel.com>,
"Piotr Luc" <piotr.luc@intel.com>,
"Tom Lendacky" <thomas.lendacky@amd.com>,
"Fenghua Yu" <fenghua.yu@intel.com>,
"Lu Baolu" <baolu.lu@linux.intel.com>,
"Reza Arbab" <arbab@linux.vnet.ibm.com>,
"David Howells" <dhowells@redhat.com>,
"Matt Fleming" <matt@codeblueprint.co.uk>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
"Laura Abbott" <labbott@redhat.com>,
"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Eric Biederman" <ebiederm@xmission.com>,
"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
"Paul Mackerras" <paulus@samba.org>,
"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Dave Airlie" <airlied@redhat.com>,
"Kees Cook" <keescook@chromium.org>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Arnd Bergmann" <arnd@arndb.de>, "Tejun Heo" <tj@kernel.org>,
"Christoph Lameter" <cl@linux.com>
Subject: Re: [RFC Part1 PATCH v3 16/17] X86/KVM: Provide support to create Guest and HV shared per-CPU variables
Date: Wed, 30 Aug 2017 11:18:42 -0500 [thread overview]
Message-ID: <0810a732-9c77-a543-ffeb-7fd2d8f46266@amd.com> (raw)
In-Reply-To: <20170829102258.gxk227js4yw47qi3@pd.tnic>
Hi Boris,
On 08/29/2017 05:22 AM, Borislav Petkov wrote:
[...]
> On Mon, Jul 24, 2017 at 02:07:56PM -0500, Brijesh Singh wrote:
>> Some KVM specific MSR's (steal-time, asyncpf, avic_eio) allocates per-CPU
>
> MSRs
>
>> variable at compile time and share its physical address with hypervisor.
>
> That sentence needs changing - the MSRs don't allocate - for them gets
> allocated.
>
>> It presents a challege when SEV is active in guest OS, when SEV is active,
>> the guest memory is encrypted with guest key hence hypervisor will not
>> able to modify the guest memory. When SEV is active, we need to clear the
>> encryption attribute (aka C-bit) of shared physical addresses so that both
>> guest and hypervisor can access the data.
>
> This whole paragraph needs rewriting.
>
I will improve the commit message in next rev.
[...]
>> +/* NOTE: function is marked as __ref because it is used by __init functions */
>
> No need for that comment.
>
> What should you look into is why do you need to call the early versions:
>
> " * producing a warning (of course, no warning does not mean code is
> * correct, so optimally document why the __ref is needed and why it's OK)."
>
> And we do have the normal set_memory_decrypted() etc helpers so why
> aren't we using those?
>
Since kvm_guest_init() is called early in the boot process hence we will not
able to use set_memory_decrypted() function. IIRC, if we try calling
set_memory_decrypted() early then we will hit a BUG_ON [1] -- mainly when it
tries to flush the caches.
[1] http://elixir.free-electrons.com/linux/latest/source/arch/x86/mm/pageattr.c#L167
> If you need to use the early ones too, then you probably need to
> differentiate this in the callers by passing a "bool early", which calls
> the proper flavor.
>
Sure I can rearrange code to make it more readable and use "bool early"
parameter to differentiate it.
>> +static int __ref kvm_map_hv_shared_decrypted(void)
>> +{
>> + static int once, ret;
>> + int cpu;
>> +
>> + if (once)
>> + return ret;
>
> So this function gets called per-CPU but you need to do this ugly "once"
> thing - i.e., global function called in a per-CPU context.
>
> Why can't you do that mapping only on the current CPU and then
> when that function is called on the next CPU, it will do the same thing
> on that next CPU?
>
Yes, it can be done but I remember running into issues during the CPU hot plug.
The patch uses early_set_memory_decrypted() -- which calls
kernel_physical_mapping_init() to split the large pages into smaller. IIRC, the
API did not work after the system is successfully booted. After the system is
booted we must use the set_memory_decrypted().
I was trying to avoid mixing early and no-early set_memory_decrypted() but if
feedback is: use early_set_memory_decrypted() only if its required otherwise
use set_memory_decrypted() then I can improve the logic in next rev. thanks
[...]
>> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
>> index da0be9a..52854cf 100644
>> --- a/include/asm-generic/vmlinux.lds.h
>> +++ b/include/asm-generic/vmlinux.lds.h
>> @@ -783,6 +783,9 @@
>> . = ALIGN(cacheline); \
>> *(.data..percpu) \
>> *(.data..percpu..shared_aligned) \
>> + . = ALIGN(PAGE_SIZE); \
>> + *(.data..percpu..hv_shared) \
>> + . = ALIGN(PAGE_SIZE); \
>> VMLINUX_SYMBOL(__per_cpu_end) = .;
>
> Yeah, no, you can't do that. That's adding this section unconditionally
> on *every* arch. You need to do some ifdeffery like it is done at the
> beginning of that file and have this only on the arch which supports SEV.
>
Will do . thanks
-Brijesh
next prev parent reply other threads:[~2017-08-30 16:19 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-24 19:07 [RFC Part1 PATCH v3 00/17] x86: Secure Encrypted Virtualization (AMD) Brijesh Singh
2017-07-24 19:07 ` [RFC Part1 PATCH v3 01/17] Documentation/x86: Add AMD Secure Encrypted Virtualization (SEV) descrption Brijesh Singh
2017-07-25 5:45 ` Borislav Petkov
2017-07-25 14:59 ` Brijesh Singh
2017-07-24 19:07 ` [RFC Part1 PATCH v3 02/17] x86/CPU/AMD: Add the Secure Encrypted Virtualization CPU feature Brijesh Singh
2017-07-25 10:26 ` Borislav Petkov
2017-07-25 14:29 ` Tom Lendacky
2017-07-25 14:36 ` Borislav Petkov
2017-07-25 14:58 ` Tom Lendacky
2017-07-25 15:13 ` Borislav Petkov
2017-07-25 15:29 ` Tom Lendacky
2017-07-25 15:33 ` Borislav Petkov
2017-08-09 18:17 ` Tom Lendacky
2017-08-17 8:12 ` Borislav Petkov
2017-07-24 19:07 ` [RFC Part1 PATCH v3 03/17] x86/mm: Secure Encrypted Virtualization (SEV) support Brijesh Singh
2017-07-26 4:28 ` Borislav Petkov
2017-07-26 16:47 ` Tom Lendacky
2017-07-27 13:39 ` Borislav Petkov
2017-07-24 19:07 ` [RFC Part1 PATCH v3 04/17] x86/mm: Don't attempt to encrypt initrd under SEV Brijesh Singh
2017-07-26 14:44 ` Borislav Petkov
2017-07-24 19:07 ` [RFC Part1 PATCH v3 05/17] x86, realmode: Don't decrypt trampoline area " Brijesh Singh
2017-07-26 16:03 ` Borislav Petkov
2017-08-10 13:03 ` Tom Lendacky
2017-07-24 19:07 ` [RFC Part1 PATCH v3 06/17] x86/mm: Use encrypted access of boot related data with SEV Brijesh Singh
2017-07-27 13:31 ` Borislav Petkov
2017-08-17 18:05 ` Tom Lendacky
2017-07-24 19:07 ` [RFC Part1 PATCH v3 07/17] x86/mm: Include SEV for encryption memory attribute changes Brijesh Singh
2017-07-27 14:58 ` Borislav Petkov
2017-07-28 8:47 ` David Laight
2017-08-17 18:21 ` Tom Lendacky
2017-08-17 18:10 ` Tom Lendacky
2017-07-24 19:07 ` [RFC Part1 PATCH v3 08/17] x86/efi: Access EFI data as encrypted when SEV is active Brijesh Singh
2017-07-28 10:31 ` Borislav Petkov
2017-08-17 18:42 ` Tom Lendacky
2017-07-24 19:07 ` [RFC Part1 PATCH v3 09/17] resource: Consolidate resource walking code Brijesh Singh
2017-07-28 15:23 ` Borislav Petkov
2017-08-17 18:55 ` Tom Lendacky
2017-08-17 19:03 ` Tom Lendacky
2017-07-24 19:07 ` [RFC Part1 PATCH v3 10/17] resource: Provide resource struct in resource walk callback Brijesh Singh
2017-07-31 8:26 ` Borislav Petkov
2017-07-31 22:19 ` Kees Cook
2017-07-24 19:07 ` [RFC Part1 PATCH v3 11/17] x86/mm, resource: Use PAGE_KERNEL protection for ioremap of memory pages Brijesh Singh
2017-08-02 4:02 ` Borislav Petkov
2017-08-17 19:22 ` Tom Lendacky
2017-07-24 19:07 ` [RFC Part1 PATCH v3 12/17] x86/mm: DMA support for SEV memory encryption Brijesh Singh
2017-08-07 3:48 ` Borislav Petkov
2017-08-17 19:35 ` Tom Lendacky
2017-07-24 19:07 ` [RFC Part1 PATCH v3 13/17] x86/io: Unroll string I/O when SEV is active Brijesh Singh
2017-07-25 9:51 ` David Laight
2017-07-26 10:45 ` Arnd Bergmann
2017-07-26 19:24 ` Brijesh Singh
2017-07-26 19:26 ` H. Peter Anvin
2017-07-26 20:07 ` Brijesh Singh
2017-07-27 7:45 ` David Laight
2017-08-22 16:52 ` Borislav Petkov
2017-09-15 12:24 ` Borislav Petkov
2017-09-15 14:13 ` Brijesh Singh
2017-09-15 14:40 ` Borislav Petkov
2017-09-15 14:48 ` Brijesh Singh
2017-09-15 16:22 ` Borislav Petkov
2017-09-15 16:27 ` Brijesh Singh
2017-07-24 19:07 ` [RFC Part1 PATCH v3 14/17] x86/boot: Add early boot support when running with SEV active Brijesh Singh
2017-08-23 15:30 ` Borislav Petkov
2017-08-24 18:54 ` Tom Lendacky
2017-08-25 12:54 ` Borislav Petkov
2017-07-24 19:07 ` [RFC Part1 PATCH v3 15/17] x86: Add support for changing memory encryption attribute in early boot Brijesh Singh
2017-08-28 10:51 ` Borislav Petkov
2017-08-28 11:49 ` Brijesh Singh
2017-07-24 19:07 ` [RFC Part1 PATCH v3 16/17] X86/KVM: Provide support to create Guest and HV shared per-CPU variables Brijesh Singh
2017-08-29 10:22 ` Borislav Petkov
2017-08-30 16:18 ` Brijesh Singh [this message]
2017-08-30 17:46 ` Borislav Petkov
2017-09-01 22:52 ` Brijesh Singh
2017-09-02 3:21 ` Andy Lutomirski
2017-09-03 2:34 ` Brijesh Singh
2017-09-04 17:05 ` Borislav Petkov
2017-09-04 17:47 ` Brijesh Singh
2017-07-24 19:07 ` [RFC Part1 PATCH v3 17/17] X86/KVM: Clear encryption attribute when SEV is active Brijesh Singh
2017-08-31 15:06 ` Borislav Petkov
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