6.6-stable review patch. If anyone has any objections, please let me know.
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From: Linus Torvalds torvalds@linux-foundation.org
[ Upstream commit e8432ac802a028eaee6b1e86383d7cd8e9fb8431 ]
We have some very fancy min/max macros that have tons of sanity checking to warn about mixed signedness etc.
This is all things that a sane compiler should warn about, but there are no sane compiler interfaces for this, and '-Wsign-compare' is broken [1] and not useful.
So then we compensate (some would say over-compensate) by doing the checks manually with some truly horrid macro games.
And no, we can't just use __builtin_types_compatible_p(), because the whole question of "does it make sense to compare these two values" is a lot more complicated than that.
For example, it makes a ton of sense to compare unsigned values with simple constants like "5", even if that is indeed a signed type. So we have these very strange macros to try to make sensible type checking decisions on the arguments to 'min()' and 'max()'.
But that can cause enormous code expansion if the min()/max() macros are used with complicated expressions, and particularly if you nest these things so that you get the first big expansion then expanded again.
The xen setup.c file ended up ballooning to over 50MB of preprocessed noise that takes 15s to compile (obviously depending on the build host), largely due to one single line.
So let's split that one single line to just be simpler. I think it ends up being more legible to humans too at the same time. Now that single file compiles in under a second.
Reported-and-reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Link: https://lore.kernel.org/all/c83c17bb-be75-4c67-979d-54eee38774c6@lucifer.loc... Link: https://staticthinking.wordpress.com/2023/07/25/wsign-compare-is-garbage/ [1] Cc: David Laight David.Laight@aculab.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Stable-dep-of: be35d91c8880 ("xen: tolerate ACPI NVS memory overlapping with Xen allocated memory") Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/xen/setup.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c index d44d6d8b33195..d2073df5c5624 100644 --- a/arch/x86/xen/setup.c +++ b/arch/x86/xen/setup.c @@ -691,6 +691,7 @@ char * __init xen_memory_setup(void) struct xen_memory_map memmap; unsigned long max_pages; unsigned long extra_pages = 0; + unsigned long maxmem_pages; int i; int op;
@@ -762,8 +763,8 @@ char * __init xen_memory_setup(void) * Make sure we have no memory above max_pages, as this area * isn't handled by the p2m management. */ - extra_pages = min3(EXTRA_MEM_RATIO * min(max_pfn, PFN_DOWN(MAXMEM)), - extra_pages, max_pages - max_pfn); + maxmem_pages = EXTRA_MEM_RATIO * min(max_pfn, PFN_DOWN(MAXMEM)); + extra_pages = min3(maxmem_pages, extra_pages, max_pages - max_pfn); i = 0; addr = xen_e820_table.entries[0].addr; size = xen_e820_table.entries[0].size;