From: "Singh, Brijesh" <brijesh.singh@amd.com>
To: Borislav Petkov <bp@alien8.de>,
"Lendacky, Thomas" <Thomas.Lendacky@amd.com>
Cc: "Singh, Brijesh" <brijesh.singh@amd.com>,
lijiang <lijiang@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"x86@kernel.org" <x86@kernel.org>,
"hpa@zytor.com" <hpa@zytor.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"dyoung@redhat.com" <dyoung@redhat.com>,
"bhe@redhat.com" <bhe@redhat.com>
Subject: Re: [PATCH 1/3] kexec: Do not map the kexec area as decrypted when SEV is active
Date: Mon, 25 Mar 2019 18:17:26 +0000 [thread overview]
Message-ID: <11013ad2-2eab-5a7a-d4e2-a9da4920cfab@amd.com> (raw)
In-Reply-To: <20190325173239.GO12016@zn.tnic>
On 3/25/19 12:32 PM, Borislav Petkov wrote:
> On Mon, Mar 25, 2019 at 05:17:55PM +0000, Singh, Brijesh wrote:
>> By default all the memory regions are mapped encrypted. The
>> set_memory_{encrypt,decrypt}() is a generic function which can be
>> called explicitly to clear/set the encryption mask from the existing
>> memory mapping. The mem_encrypt_active() returns true if either SEV or
>> SME is active. So the __set_memory_enc_dec() uses the
>> memory_encrypt_active() check to ensure that the function is no-op when
>> SME/SEV are not active.
>>
>> Currently, the arch_kexec_post_alloc_pages() unconditionally clear the
>> encryption mask from the kexec area. In case of SEV, we should not clear
>> the encryption mask.
>
> Brijesh, I know all that.
>
> Please read what I said here at the end:
>
> https://lkml.kernel.org/r/20190324150034.GH23289@zn.tnic
>
> With this change, the code looks like this:
>
> + if (sme_active())
> + return set_memory_decrypted((unsigned long)vaddr, pages);
>
> now in __set_memory_enc_dec via set_memory_decrypted():
>
> /* Nothing to do if memory encryption is not active */
> if (!mem_encrypt_active())
> return 0;
>
>
> so you have:
>
> if (sme_active())
>
> ...
>
> if (!mem_encrypt_active())
>
>
> now maybe this is all clear to you and Tom but I betcha others will get
> confused. Probably something like "well, what should be active now, SME,
> SEV or memory encryption in general"?
>
> I hope you're catching my drift.
>
> So if you want to *not* decrypt memory in the SEV case, then doing something
> like this should make it a bit more clear:
>
>
> if (sev_active())
> return;
>
> return set_memory_decrypted((unsigned long)vaddr, pages);
>
I see your point. I agree it can get confusing.
> along with a comment *why* we're checking here.
>
> But actually, I'd prefer if you had separate wrappers which are called
> for SME and for SEV.
Just a thought, maybe we can move the above if(sev_active()) check up in
kernel/kexec_core.c because we don't need to set/clear the encryption
masks when SEV is active so there is no need to call the wrapper.
>
> I'll let Tom chime in too.
>
next prev parent reply other threads:[~2019-03-25 18:17 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-15 10:32 [PATCH 0/3] Add kdump support for the SEV enabled guest Lianbo Jiang
2019-03-15 10:32 ` [PATCH 1/3] kexec: Do not map the kexec area as decrypted when SEV is active Lianbo Jiang
2019-03-24 15:00 ` Borislav Petkov
2019-03-25 1:58 ` lijiang
2019-03-25 6:37 ` Borislav Petkov
2019-03-25 17:17 ` Singh, Brijesh
2019-03-25 17:32 ` Borislav Petkov
2019-03-25 18:17 ` Singh, Brijesh [this message]
2019-03-25 19:59 ` Lendacky, Thomas
2019-03-26 10:06 ` Boris Petkov
2019-03-26 1:27 ` lijiang
2019-03-15 10:32 ` [PATCH 2/3] kexec: Set the C-bit in the identity map page table " Lianbo Jiang
2019-03-15 10:32 ` [PATCH 3/3] kdump,proc/vmcore: Enable kdumping encrypted memory when SEV was active Lianbo Jiang
2019-03-15 10:42 ` [PATCH 0/3] Add kdump support for the SEV enabled guest lijiang
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