From: Ashish Kalra ashish.kalra@amd.com
When the shared pages are being made private during kdump preparation there are additional checks to handle shared GHCB pages.
These additional checks include handling the case of GHCB page being contained within a huge page.
The check for handling the case of GHCB contained within a huge page incorrectly skips a page just below the GHCB page from being transitioned back to private during kdump preparation.
This skipped page causes a 0x404 #VC exception when it is accessed later while dumping guest memory during vmcore generation via kdump.
Correct the range to be checked for GHCB contained in a huge page. Also ensure that the skipped huge page containing the GHCB page is transitioned back to private by applying the correct address mask later when changing GHCBs to private at end of kdump preparation.
Fixes: 3074152e56c9 ("x86/sev: Convert shared memory back to private on kexec") Cc: stable@vger.kernel.org Signed-off-by: Ashish Kalra ashish.kalra@amd.com --- arch/x86/coco/sev/core.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c index d35fec7b164a..30b74e4e4e88 100644 --- a/arch/x86/coco/sev/core.c +++ b/arch/x86/coco/sev/core.c @@ -1019,7 +1019,8 @@ static void unshare_all_memory(void) data = per_cpu(runtime_data, cpu); ghcb = (unsigned long)&data->ghcb_page;
- if (addr <= ghcb && ghcb <= addr + size) { + /* Handle the case of a huge page containing the GHCB page */ + if (addr <= ghcb && ghcb < addr + size) { skipped_addr = true; break; } @@ -1131,8 +1132,8 @@ static void shutdown_all_aps(void) void snp_kexec_finish(void) { struct sev_es_runtime_data *data; + unsigned long size, addr; unsigned int level, cpu; - unsigned long size; struct ghcb *ghcb; pte_t *pte;
@@ -1160,8 +1161,10 @@ void snp_kexec_finish(void) ghcb = &data->ghcb_page; pte = lookup_address((unsigned long)ghcb, &level); size = page_level_size(level); - set_pte_enc(pte, level, (void *)ghcb); - snp_set_memory_private((unsigned long)ghcb, (size / PAGE_SIZE)); + /* Handle the case of a huge page containing the GHCB page */ + addr = (unsigned long)ghcb & page_level_mask(level); + set_pte_enc(pte, level, (void *)addr); + snp_set_memory_private(addr, (size / PAGE_SIZE)); } }
On Tue, May 06, 2025 at 06:35:29PM +0000, Ashish Kalra wrote:
From: Ashish Kalra ashish.kalra@amd.com
When the shared pages are being made private during kdump preparation there are additional checks to handle shared GHCB pages.
These additional checks include handling the case of GHCB page being contained within a huge page.
The check for handling the case of GHCB contained within a huge page incorrectly skips a page just below the GHCB page from being transitioned back to private during kdump preparation.
This skipped page causes a 0x404 #VC exception when it is accessed later while dumping guest memory during vmcore generation via kdump.
Correct the range to be checked for GHCB contained in a huge page. Also ensure that the skipped huge page containing the GHCB page is transitioned back to private by applying the correct address mask later when changing GHCBs to private at end of kdump preparation.
Fixes: 3074152e56c9 ("x86/sev: Convert shared memory back to private on kexec") Cc: stable@vger.kernel.org Signed-off-by: Ashish Kalra ashish.kalra@amd.com
arch/x86/coco/sev/core.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
Ok, I've pushed both patches here:
https://git.kernel.org/pub/scm/linux/kernel/git/bp/bp.git/log/?h=tip-x86-urg...
Please have those who are affected by the issues test and report back.
Thx.
On 5/7/2025 3:12 PM, Borislav Petkov wrote:
On Tue, May 06, 2025 at 06:35:29PM +0000, Ashish Kalra wrote:
From: Ashish Kalra ashish.kalra@amd.com
When the shared pages are being made private during kdump preparation there are additional checks to handle shared GHCB pages.
These additional checks include handling the case of GHCB page being contained within a huge page.
The check for handling the case of GHCB contained within a huge page incorrectly skips a page just below the GHCB page from being transitioned back to private during kdump preparation.
This skipped page causes a 0x404 #VC exception when it is accessed later while dumping guest memory during vmcore generation via kdump.
Correct the range to be checked for GHCB contained in a huge page. Also ensure that the skipped huge page containing the GHCB page is transitioned back to private by applying the correct address mask later when changing GHCBs to private at end of kdump preparation.
Fixes: 3074152e56c9 ("x86/sev: Convert shared memory back to private on kexec") Cc: stable@vger.kernel.org Signed-off-by: Ashish Kalra ashish.kalra@amd.com
arch/x86/coco/sev/core.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
Ok, I've pushed both patches here:
https://git.kernel.org/pub/scm/linux/kernel/git/bp/bp.git/log/?h=tip-x86-urg...
Please have those who are affected by the issues test and report back.
Thx.
I tested the failure scenario with the patch hosted in the referenced Git tree [1]. The patch resolves the issue.
Tested-by: Srikanth Aithal sraithal@amd.com
[1]: https://git.kernel.org/pub/scm/linux/kernel/git/bp/bp.git/log/?h=tip-x86-urg...
On 5/6/25 13:35, Ashish Kalra wrote:
From: Ashish Kalra ashish.kalra@amd.com
When the shared pages are being made private during kdump preparation there are additional checks to handle shared GHCB pages.
These additional checks include handling the case of GHCB page being contained within a huge page.
The check for handling the case of GHCB contained within a huge page incorrectly skips a page just below the GHCB page from being transitioned back to private during kdump preparation.
This skipped page causes a 0x404 #VC exception when it is accessed later while dumping guest memory during vmcore generation via kdump.
Correct the range to be checked for GHCB contained in a huge page. Also ensure that the skipped huge page containing the GHCB page is transitioned back to private by applying the correct address mask later when changing GHCBs to private at end of kdump preparation.
Fixes: 3074152e56c9 ("x86/sev: Convert shared memory back to private on kexec") Cc: stable@vger.kernel.org Signed-off-by: Ashish Kalra ashish.kalra@amd.com
Reviewed-by: Tom Lendacky thomas.lendacky@amd.com
arch/x86/coco/sev/core.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c index d35fec7b164a..30b74e4e4e88 100644 --- a/arch/x86/coco/sev/core.c +++ b/arch/x86/coco/sev/core.c @@ -1019,7 +1019,8 @@ static void unshare_all_memory(void) data = per_cpu(runtime_data, cpu); ghcb = (unsigned long)&data->ghcb_page;
if (addr <= ghcb && ghcb <= addr + size) {
/* Handle the case of a huge page containing the GHCB page */if (addr <= ghcb && ghcb < addr + size) { skipped_addr = true; break; }@@ -1131,8 +1132,8 @@ static void shutdown_all_aps(void) void snp_kexec_finish(void) { struct sev_es_runtime_data *data;
- unsigned long size, addr; unsigned int level, cpu;
- unsigned long size; struct ghcb *ghcb; pte_t *pte;
@@ -1160,8 +1161,10 @@ void snp_kexec_finish(void) ghcb = &data->ghcb_page; pte = lookup_address((unsigned long)ghcb, &level); size = page_level_size(level);
set_pte_enc(pte, level, (void *)ghcb);snp_set_memory_private((unsigned long)ghcb, (size / PAGE_SIZE));
/* Handle the case of a huge page containing the GHCB page */addr = (unsigned long)ghcb & page_level_mask(level);set_pte_enc(pte, level, (void *)addr);snp_set_memory_private(addr, (size / PAGE_SIZE));}
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 82b7f88f2316c5442708daeb0b5ec5aa54c8ff7f Gitweb: https://git.kernel.org/tip/82b7f88f2316c5442708daeb0b5ec5aa54c8ff7f Author: Ashish Kalra ashish.kalra@amd.com AuthorDate: Tue, 06 May 2025 18:35:29 Committer: Borislav Petkov (AMD) bp@alien8.de CommitterDate: Tue, 13 May 2025 19:47:48 +02:00
x86/sev: Make sure pages are not skipped during kdump
When shared pages are being converted to private during kdump, additional checks are performed. They include handling the case of a GHCB page being contained within a huge page.
Currently, this check incorrectly skips a page just below the GHCB page from being transitioned back to private during kdump preparation.
This skipped page causes a 0x404 #VC exception when it is accessed later while dumping guest memory for vmcore generation.
Correct the range to be checked for GHCB contained in a huge page. Also, ensure that the skipped huge page containing the GHCB page is transitioned back to private by applying the correct address mask later when changing GHCBs to private at end of kdump preparation.
[ bp: Massage commit message. ]
Fixes: 3074152e56c9 ("x86/sev: Convert shared memory back to private on kexec") Signed-off-by: Ashish Kalra ashish.kalra@amd.com Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Reviewed-by: Tom Lendacky thomas.lendacky@amd.com Tested-by: Srikanth Aithal sraithal@amd.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/20250506183529.289549-1-Ashish.Kalra@amd.com --- arch/x86/coco/sev/core.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c index 41060ba..36beaac 100644 --- a/arch/x86/coco/sev/core.c +++ b/arch/x86/coco/sev/core.c @@ -1101,7 +1101,8 @@ static void unshare_all_memory(void) data = per_cpu(runtime_data, cpu); ghcb = (unsigned long)&data->ghcb_page;
- if (addr <= ghcb && ghcb <= addr + size) { + /* Handle the case of a huge page containing the GHCB page */ + if (addr <= ghcb && ghcb < addr + size) { skipped_addr = true; break; } @@ -1213,8 +1214,8 @@ static void shutdown_all_aps(void) void snp_kexec_finish(void) { struct sev_es_runtime_data *data; + unsigned long size, addr; unsigned int level, cpu; - unsigned long size; struct ghcb *ghcb; pte_t *pte;
@@ -1242,8 +1243,10 @@ void snp_kexec_finish(void) ghcb = &data->ghcb_page; pte = lookup_address((unsigned long)ghcb, &level); size = page_level_size(level); - set_pte_enc(pte, level, (void *)ghcb); - snp_set_memory_private((unsigned long)ghcb, (size / PAGE_SIZE)); + /* Handle the case of a huge page containing the GHCB page */ + addr = (unsigned long)ghcb & page_level_mask(level); + set_pte_enc(pte, level, (void *)addr); + snp_set_memory_private(addr, (size / PAGE_SIZE)); } }
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