[PATCH v6.6-v6.1] x86/mm/ident_map: Use gbpages only where full GB page should be mapped.
From: Steve Wahl steve.wahl@hpe.com
[ Upstream commit cc31744a294584a36bf764a0ffa3255a8e69f036 ]
When ident_pud_init() uses only GB pages to create identity maps, large ranges of addresses not actually requested can be included in the resulting table; a 4K request will map a full GB. This can include a lot of extra address space past that requested, including areas marked reserved by the BIOS. That allows processor speculation into reserved regions, that on UV systems can cause system halts.
Only use GB pages when map creation requests include the full GB page of space. Fall back to using smaller 2M pages when only portions of a GB page are included in the request.
No attempt is made to coalesce mapping requests. If a request requires a map entry at the 2M (pmd) level, subsequent mapping requests within the same 1G region will also be at the pmd level, even if adjacent or overlapping such requests could have been combined to map a full GB page. Existing usage starts with larger regions and then adds smaller regions, so this should not have any great consequence.
Signed-off-by: Steve Wahl steve.wahl@hpe.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Pavin Joseph me@pavinjoseph.com Tested-by: Sarah Brofeldt srhb@dbc.dk Tested-by: Eric Hagberg ehagberg@gmail.com Link: https://lore.kernel.org/all/20240717213121.3064030-3-steve.wahl@hpe.com Signed-off-by: Bruno VERNAY bruno.vernay@se.com Signed-off-by: Hugo SIMELIERE hsimeliere.opensource@witekio.com --- arch/x86/mm/ident_map.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-)
diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c index 968d7005f4a7..a204a332c71f 100644 --- a/arch/x86/mm/ident_map.c +++ b/arch/x86/mm/ident_map.c @@ -26,18 +26,31 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page, for (; addr < end; addr = next) { pud_t *pud = pud_page + pud_index(addr); pmd_t *pmd; + bool use_gbpage;
next = (addr & PUD_MASK) + PUD_SIZE; if (next > end) next = end;
- if (info->direct_gbpages) { - pud_t pudval; + /* if this is already a gbpage, this portion is already mapped */ + if (pud_leaf(*pud)) + continue; + + /* Is using a gbpage allowed? */ + use_gbpage = info->direct_gbpages;
- if (pud_present(*pud)) - continue; + /* Don't use gbpage if it maps more than the requested region. */ + /* at the begining: */ + use_gbpage &= ((addr & ~PUD_MASK) == 0); + /* ... or at the end: */ + use_gbpage &= ((next & ~PUD_MASK) == 0); + + /* Never overwrite existing mappings */ + use_gbpage &= !pud_present(*pud); + + if (use_gbpage) { + pud_t pudval;
- addr &= PUD_MASK; pudval = __pud((addr - info->offset) | info->page_flag); set_pud(pud, pudval); continue;
On Mon, Feb 10, 2025 at 09:56:09AM +0100, hsimeliere.opensource@witekio.com wrote:
From: Steve Wahl steve.wahl@hpe.com
[ Upstream commit cc31744a294584a36bf764a0ffa3255a8e69f036 ]
When ident_pud_init() uses only GB pages to create identity maps, large ranges of addresses not actually requested can be included in the resulting table; a 4K request will map a full GB. This can include a lot of extra address space past that requested, including areas marked reserved by the BIOS. That allows processor speculation into reserved regions, that on UV systems can cause system halts.
Only use GB pages when map creation requests include the full GB page of space. Fall back to using smaller 2M pages when only portions of a GB page are included in the request.
No attempt is made to coalesce mapping requests. If a request requires a map entry at the 2M (pmd) level, subsequent mapping requests within the same 1G region will also be at the pmd level, even if adjacent or overlapping such requests could have been combined to map a full GB page. Existing usage starts with larger regions and then adds smaller regions, so this should not have any great consequence.
Signed-off-by: Steve Wahl steve.wahl@hpe.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Pavin Joseph me@pavinjoseph.com Tested-by: Sarah Brofeldt srhb@dbc.dk Tested-by: Eric Hagberg ehagberg@gmail.com Link: https://lore.kernel.org/all/20240717213121.3064030-3-steve.wahl@hpe.com Signed-off-by: Bruno VERNAY bruno.vernay@se.com Signed-off-by: Hugo SIMELIERE hsimeliere.opensource@witekio.com
arch/x86/mm/ident_map.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-)
diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c index 968d7005f4a7..a204a332c71f 100644 --- a/arch/x86/mm/ident_map.c +++ b/arch/x86/mm/ident_map.c @@ -26,18 +26,31 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page, for (; addr < end; addr = next) { pud_t *pud = pud_page + pud_index(addr); pmd_t *pmd;
bool use_gbpage;next = (addr & PUD_MASK) + PUD_SIZE; if (next > end) next = end;
if (info->direct_gbpages) {pud_t pudval;
/* if this is already a gbpage, this portion is already mapped */if (pud_leaf(*pud))continue;/* Is using a gbpage allowed? */use_gbpage = info->direct_gbpages;
if (pud_present(*pud))continue;
/* Don't use gbpage if it maps more than the requested region. *//* at the begining: */use_gbpage &= ((addr & ~PUD_MASK) == 0);/* ... or at the end: */use_gbpage &= ((next & ~PUD_MASK) == 0);/* Never overwrite existing mappings */use_gbpage &= !pud_present(*pud);if (use_gbpage) {pud_t pudval;
addr &= PUD_MASK; pudval = __pud((addr - info->offset) | info->page_flag); set_pud(pud, pudval); continue;-- 2.43.0
Why are you wanting this commit to be backported to these kernel branches, when the developers explicitly asked for it to NOT be applied there? What problem is this fixing that you have determined that it should be backported?
And most importantly, how did you test this?
thanks,
greg k-h
linux-stable-mirror@lists.linaro.org
-
Greg KH -
hsimeliere.opensourceďź witekio.com