On Thu, Sep 06, 2018 at 10:13:00AM +0200, Peter Zijlstra wrote:
> No, you got it the first time. There are in fact more fixmap abusers;
> see drivers/acpi/apei/ghes.c. Also, as long as set_fixmap() allows
> overwriting a _PAGE_PRESENT pte and has that dodgy
> __flush_tlb_one_kernel() in it, the broken remains (and can return).
>
> So we need to fix fixmap, to either disallow overwriting a _PAGE_PRESENT
> pte, or to issue a full TLB invalidate.
>
> Either fix will terminally break GHES, but that's OK, they've known
> about this issue since 2015 and haven't cared, so I can't be bothered
> about them.
The below, combined with your text_poke() patches (text_poke disabled
IRQs, so the below still complains, and I was lazy) makes my machine
(mostly) happy.
There's still some complaining before the poking_mm exists. Let me see
if I can't cure that.
---
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index dd519f372169..8df85fe66332 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -259,15 +260,27 @@ static pte_t *fill_pte(pmd_t *pmd, unsigned long vaddr)
static void __set_pte_vaddr(pud_t *pud, unsigned long vaddr, pte_t new_pte)
{
pmd_t *pmd = fill_pmd(pud, vaddr);
- pte_t *pte = fill_pte(pmd, vaddr);
+ pte_t *ptep = fill_pte(pmd, vaddr);
- set_pte(pte, new_pte);
+ pte_t pte = *ptep;
- /*
- * It's enough to flush this one mapping.
- * (PGE mappings get flushed as well)
- */
- __flush_tlb_one_kernel(vaddr);
+ set_pte(ptep, new_pte);
+
+ if (irqs_disabled()) {
+ WARN((pte_val(pte) & _PAGE_PRESENT) && (pte_val(pte) != pte_val(new_pte)),
+ "set_fixmap(%d, %lx), was: %lx",
+ (int)__virt_to_fix(vaddr),
+ pte_val(new_pte), pte_val(pte));
+
+ /*
+ * It is _NOT_ enough to flush just the local mapping;
+ * it might mostly work, but there is no guarantee a remote
+ * CPU didn't load this entry into its TLB.
+ */
+ __flush_tlb_one_kernel(vaddr);
+ } else {
+ flush_tlb_kernel_range(vaddr, vaddr + PAGE_SIZE);
+ }
}
void set_pte_vaddr_p4d(p4d_t *p4d_page, unsigned long vaddr, pte_t new_pte)
diff --git a/drivers/acpi/apei/Kconfig b/drivers/acpi/apei/Kconfig
index 52ae5438edeb..e3c415bdbfbf 100644
--- a/drivers/acpi/apei/Kconfig
+++ b/drivers/acpi/apei/Kconfig
@@ -19,6 +19,7 @@ config ACPI_APEI
config ACPI_APEI_GHES
bool "APEI Generic Hardware Error Source"
+ depends on BROKEN
depends on ACPI_APEI
select ACPI_HED
select IRQ_WORK
