Messages in this thread | | | Date | Mon, 2 Aug 2021 13:19:48 +0100 | From | Catalin Marinas <> | Subject | Re: [RFC PATCH 1/2] arm64: mm: Make virt_addr_valid to check for pfn_valid again |
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Adding Mike and Anshuman,
On Wed, Jul 28, 2021 at 07:44:15PM +0300, Oleksandr Tyshchenko wrote: > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > > The problem is that Arm's implementation of virt_addr_valid() > leads to memblock_is_map_memory() check, which will fail for > ZONE_DEVICE based addresses. But, the pfn_valid() check in turn > is able to cope with ZONE_DEVICE based memory. > > You can find a good explanation of that problem at: > https://lore.kernel.org/lkml/1614921898-4099-2-git-send-email-anshuman.khandual@arm.com > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> > --- > I am not quite sure whether it is a "correct" place and > the change itself, I just partially restored a behaviour before: > https://lore.kernel.org/lkml/20210511100550.28178-4-rppt@kernel.org > So, the target of this patch is to get a feedback how to resolve > this properly if, of course, this really needs to be resolved > (I might miss important bits here). > > It is worth mentioning that patch doesn't fix the current code base > (if I am not mistaken, no one calls virt_addr_valid() on Arm64 for > ZONE_DEVICE based addresses at the moment, so it seems that nothing > is broken), the fix is intended for the subsequent patch in this > series that will try to enable Xen's "unpopulated-alloc" usage > on Arm (it was enabled on x86 so far). > Please see: > [RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide > unallocated space > > The subsequent patch will enable the code where virt_addr_valid() > is used in drivers/xen/unpopulated-alloc.c:fill_list() to check that > a virtual address returned by memremap_pages() is valid.
I wonder what the point of calling virt_addr_valid() in fill_list() is? If memremap_pages() succeeded, the pages were mapped at the returned vaddr, there's no need for an additional virt_addr_valid() check.
> --- > arch/arm64/include/asm/memory.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > index 824a365..1a35a44 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -351,7 +351,7 @@ static inline void *phys_to_virt(phys_addr_t x) > > #define virt_addr_valid(addr) ({ \ > __typeof__(addr) __addr = __tag_reset(addr); \ > - __is_lm_address(__addr) && pfn_is_map_memory(virt_to_pfn(__addr)); \ > + __is_lm_address(__addr) && pfn_valid(virt_to_pfn(__addr)); \ > })
pfn_valid() only guarantees the presence of a struct page but not necessarily that the virtual address is accessible (valid). So this change would break the NOMAP ranges case.
-- Catalin
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