From: Dexuan Cui <decui@microsoft.com>
To: Tom Lendacky <thomas.lendacky@amd.com>,
Borislav Petkov <bp@alien8.de>,
"sandipan.das@amd.com" <sandipan.das@amd.com>,
"Gupta, Pankaj" <pankaj.gupta@amd.com>,
"ray.huang@amd.com" <ray.huang@amd.com>,
"brijesh.singh@amd.com" <brijesh.singh@amd.com>,
"michael.roth@amd.com" <michael.roth@amd.com>,
"thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>
Cc: Tianyu Lan <Tianyu.Lan@microsoft.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Does earlyprintk=ttyS0 work for an AMD SNP guest on KVM?
Date: Thu, 16 Feb 2023 04:40:14 +0000 [thread overview]
Message-ID: <SA1PR21MB13359DBABC5625368E369A42BFA09@SA1PR21MB1335.namprd21.prod.outlook.com> (raw)
Hi all,
With the earlyprintk=ttyS0 kernel parameter, a C-bit mode Linux SNP guest
on Hyper-V always decides to crash via sev_es_terminate() in
do_boot_stage2_vc(), because early_setup_ghcb() fails:
early_setup_ghcb() ->
set_page_decrypted() ->
set_clr_page_flags() ->
split_large_pmd() ->
alloc_pgt_page() fails to allocate memory.
static void *alloc_pgt_page(void *context)
{
...
/* Validate there is space available for a new page. */
if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
...
return NULL;
}
...
}
alloc_pgt_page() fails to allocate memory because both
pages->pgt_buf_offset and pages->pgt_buf_size are zero.
pgt_data.pgt_buf_size is zero because of this line in
initialize_identity_maps()
pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
void initialize_identity_maps(void *rmode)
{
...
top_level_pgt = read_cr3_pa();
if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {
pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
} else {
pgt_data.pgt_buf = _pgtable;
pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);
}
In arch/x86/include/asm/boot.h, BOOT_PGT_SIZE equals
BOOT_INIT_PGT_SIZE if CONFIG_RANDOMIZE_BASE is not defined
(which is my case):
# define BOOT_INIT_PGT_SIZE (6*4096)
# ifdef CONFIG_RANDOMIZE_BASE
...
# ifdef CONFIG_X86_VERBOSE_BOOTUP
# define BOOT_PGT_SIZE (19*4096)
# else /* !CONFIG_X86_VERBOSE_BOOTUP */
# define BOOT_PGT_SIZE (17*4096)
# endif
# else /* !CONFIG_RANDOMIZE_BASE */
# define BOOT_PGT_SIZE BOOT_INIT_PGT_SIZE
# endif
I think this means: if CONFIG_RANDOMIZE_BASE is not defined,
earlyprintk=ttyS0 also doesn't work for an SNP guest on KVM?
Sorry I don't have a KVM environment at hand to test it.
If I define CONFIG_RANDOMIZE_BASE, my C-bit mode SNP guest crashes
even ealier -- it looks like CONFIG_RANDOMIZE_BASE is incompatible
with my guest on Hyper-V due to some reason I don't know.
Do you always use CONFIG_RANDOMIZE_BASE for a SNP guest on KVM
and does earlyprintk=ttyS0 work for you?
Can you please share your thoughts? Thanks!
Thanks,
-- Dexuan
next reply other threads:[~2023-02-16 4:40 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-16 4:40 Dexuan Cui [this message]
2023-02-16 9:14 ` Does earlyprintk=ttyS0 work for an AMD SNP guest on KVM? Jeremi Piotrowski
2023-02-16 17:58 ` Dexuan Cui
2023-02-17 12:51 ` Jeremi Piotrowski
2023-02-18 2:54 ` Dexuan Cui
2023-03-17 18:07 ` Tom Lendacky
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=SA1PR21MB13359DBABC5625368E369A42BFA09@SA1PR21MB1335.namprd21.prod.outlook.com \
--to=decui@microsoft.com \
--cc=Tianyu.Lan@microsoft.com \
--cc=bp@alien8.de \
--cc=brijesh.singh@amd.com \
--cc=kvm@vger.kernel.org \
--cc=linux-hyperv@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=michael.roth@amd.com \
--cc=pankaj.gupta@amd.com \
--cc=ray.huang@amd.com \
--cc=sandipan.das@amd.com \
--cc=thomas.lendacky@amd.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).