From: Kairui Song <kasong@redhat.com>
To: Thomas.Lendacky@amd.com
Cc: Baoquan He <bhe@redhat.com>,
bp@suse.de, brijesh.singh@amd.com, x86@kernel.org,
kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
mingo@redhat.com, hpa@zytor.com, tglx@linutronix.de,
Dave Young <dyoung@redhat.com>
Subject: Re: [PATCH] x86/boot: Fix kexec booting failure after SEV early boot support
Date: Wed, 26 Sep 2018 18:52:33 +0800 [thread overview]
Message-ID: <CACPcB9efDdBGnU53wRLw8uP0fzLcq0c2O8V3z=8xW_DMSOUtYw@mail.gmail.com> (raw)
In-Reply-To: <20180926073252.GC2555@MiWiFi-R3L-srv>
On Wed, Sep 26, 2018 at 3:33 PM Baoquan He <bhe@redhat.com> 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.
>
> 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)
That is much cleaner indeed, I'm not sure if enc_bit have any other
usage, if not we can just drop it for sure.
Hi Thomas, can you help confirm if enc_bit is only a cache to avoid
doing the cpuid stuff?
--
Best Regards,
Kairui Song
next prev parent reply other threads:[~2018-09-26 10:52 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 [this message]
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
2018-09-27 12:38 Kairui Song
2018-09-27 13:16 ` Lendacky, Thomas
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