From: Baoquan He <bhe@redhat.com>
To: "Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
Kairui Song <kasong@redhat.com>
Cc: Borislav Petkov <bp@suse.de>,
"Singh, Brijesh" <brijesh.singh@amd.com>,
"x86@kernel.org" <x86@kernel.org>,
"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"dyoung@redhat.com" <dyoung@redhat.com>
Subject: Re: [PATCH] x86/boot: Fix kexec booting failure after SEV early boot support
Date: Wed, 26 Sep 2018 21:21:18 +0800 [thread overview]
Message-ID: <20180926132118.GF2555@MiWiFi-R3L-srv> (raw)
In-Reply-To: <3b41fee3-e2f6-2e36-d2ca-1074c5f62bb8@amd.com>
On 09/26/18 at 01:01pm, Lendacky, Thomas wrote:
> On 09/26/2018 06:22 AM, Baoquan He wrote:
> > On 09/26/18 at 03:32pm, Baoquan He wrote:
> >> On 09/25/18 at 07:26pm, Borislav Petkov wrote:
> >>> IINM, the problem can be addressed in a simpler way by getting rid of
> >>> enc_bit and thus getting rid of the need to do relative addressing of
> >>> anything and simply doing the whole dance of figuring out the C-bit each
> >>> time. It probably wouldn't be even measurable...
> >>
> >> Couldn't agree more.
> >>
> >> Obviously enc_bit is redundent here. We only check eax each time,
> >> removing it can fix the RIP-relative addressing issue in kexec.
> >
> > OK, in distros CONFIG_AMD_MEM_ENCRYPT=y is set by default usually.
> > enc_bit can save once in normal boot, then fetch and skip the cpuid
> > detection in initialize_identity_maps(). However this only speeds up in
> > amd system with SME, on intel cpu and amd cpu w/o sme, it still needs to
> > do cpuid twice. Removing it should be not measurable as Boris said.
> > Not sure if Tom has other concern.
>
> No concern from me. The original version of the patch did not cache the
> value, that was added based on the patch series feedback. So, if there
> is no concern about executing some extra CPUID/RDMSR instructions, then
> it would certainly simplify the code quite a bit.
OK, thanks for confirming this, Tom.
Then, maybe Kairui can repost below code with formal patch log after
testing. I have tested on a intel machine with 48G memory, and
CONFIG_AMD_MEM_ENCRYPT=y, it works well. Maybe add Boris's Suggested-By,
and CC me.
Thanks
Baoquan
> >>
> >> diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
> >> index eaa843a52907..0b60eb867d25 100644
> >> --- a/arch/x86/boot/compressed/mem_encrypt.S
> >> +++ b/arch/x86/boot/compressed/mem_encrypt.S
> >> @@ -27,19 +27,6 @@ ENTRY(get_sev_encryption_bit)
> >> push %edx
> >> push %edi
> >>
> >> - /*
> >> - * RIP-relative addressing is needed to access the encryption bit
> >> - * variable. Since we are running in 32-bit mode we need this call/pop
> >> - * sequence to get the proper relative addressing.
> >> - */
> >> - call 1f
> >> -1: popl %edi
> >> - subl $1b, %edi
> >> -
> >> - movl enc_bit(%edi), %eax
> >> - cmpl $0, %eax
> >> - jge .Lsev_exit
> >> -
> >> /* Check if running under a hypervisor */
> >> movl $1, %eax
> >> cpuid
> >> @@ -69,12 +56,10 @@ ENTRY(get_sev_encryption_bit)
> >>
> >> movl %ebx, %eax
> >> andl $0x3f, %eax /* Return the encryption bit location */
> >> - movl %eax, enc_bit(%edi)
> >> jmp .Lsev_exit
> >>
> >> .Lno_sev:
> >> xor %eax, %eax
> >> - movl %eax, enc_bit(%edi)
> >>
> >> .Lsev_exit:
> >> pop %edi
> >> @@ -113,9 +98,6 @@ ENTRY(set_sev_encryption_mask)
> >> ENDPROC(set_sev_encryption_mask)
> >>
> >> .data
> >> -enc_bit:
> >> - .int 0xffffffff
> >> -
> >> #ifdef CONFIG_AMD_MEM_ENCRYPT
> >> .balign 8
> >> GLOBAL(sme_me_mask)
next prev parent reply other threads:[~2018-09-26 13:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-25 11:10 [PATCH] x86/boot: Fix kexec booting failure after SEV early boot support Kairui Song
2018-09-25 14:33 ` Lendacky, Thomas
2018-09-25 17:26 ` Borislav Petkov
2018-09-26 7:32 ` Baoquan He
2018-09-26 10:52 ` Kairui Song
2018-09-26 11:22 ` Baoquan He
2018-09-26 13:01 ` Lendacky, Thomas
2018-09-26 13:18 ` Borislav Petkov
2018-09-26 13:21 ` Baoquan He [this message]
2018-09-27 12:38 Kairui Song
2018-09-27 13:16 ` Lendacky, Thomas
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