On Thu 23-08-18 15:44:18, Vlastimil Babka wrote: > Two users have reported [1] that they have an "extremely unlikely" system > with more than MAX_PA/2 memory and L1TF mitigation is not effective. In fact > it's a CPU with 36bits phys limit (64GB) and 32GB memory, but due to holes > in the e820 map, the main region is almost 500MB over the 32GB limit: > > [ 0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000081effffff] usable > > Suggestions to use 'mem=32G' to prefer L1TF mitigation while losing the 500MB > revealed, that there's an off-by-one error in the check in > l1tf_select_mitigation(). l1tf_pfn_limit() returns the last usable pfn > (inclusive), but it's more common and hopefully less error-prone to return the > first pfn that's over limit, so this patch changes that and updates the other > callers. > > [1] https://bugzilla.suse.com/show_bug.cgi?id=1105536 > > Reported-by: George Anchev <studio@xxxxxxxxxx> > Reported-by: Christopher Snowhill <kode54@xxxxxxxxx> > Fixes: 17dbca119312 ("x86/speculation/l1tf: Add sysfs reporting for l1tf") > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Yes this should be less error prone. Acked-by: Michal Hocko <mhocko@xxxxxxxx> > --- > arch/x86/include/asm/processor.h | 2 +- > arch/x86/mm/init.c | 2 +- > arch/x86/mm/mmap.c | 2 +- > 3 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h > index a0a52274cb4a..c24297268ebc 100644 > --- a/arch/x86/include/asm/processor.h > +++ b/arch/x86/include/asm/processor.h > @@ -183,7 +183,7 @@ extern void cpu_detect(struct cpuinfo_x86 *c); > > static inline unsigned long long l1tf_pfn_limit(void) > { > - return BIT_ULL(boot_cpu_data.x86_phys_bits - 1 - PAGE_SHIFT) - 1; > + return BIT_ULL(boot_cpu_data.x86_phys_bits - 1 - PAGE_SHIFT); > } > > extern void early_cpu_init(void); > diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c > index 02de3d6065c4..63a6f9fcaf20 100644 > --- a/arch/x86/mm/init.c > +++ b/arch/x86/mm/init.c > @@ -923,7 +923,7 @@ unsigned long max_swapfile_size(void) > > if (boot_cpu_has_bug(X86_BUG_L1TF)) { > /* Limit the swap file size to MAX_PA/2 for L1TF workaround */ > - unsigned long long l1tf_limit = l1tf_pfn_limit() + 1; > + unsigned long long l1tf_limit = l1tf_pfn_limit(); > /* > * We encode swap offsets also with 3 bits below those for pfn > * which makes the usable limit higher. > diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c > index f40ab8185d94..1e95d57760cf 100644 > --- a/arch/x86/mm/mmap.c > +++ b/arch/x86/mm/mmap.c > @@ -257,7 +257,7 @@ bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot) > /* If it's real memory always allow */ > if (pfn_valid(pfn)) > return true; > - if (pfn > l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN)) > + if (pfn >= l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN)) > return false; > return true; > } > -- > 2.18.0 -- Michal Hocko SUSE Labs
