Message ID | 20230710204339.3554919-1-willy@infradead.org (mailing list archive) |
---|---|
Headers | show |
Series | New page table range API | expand |
Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle): > This patchset changes the API used by the MM to set up page table entries. > The four APIs are: > set_ptes(mm, addr, ptep, pte, nr) > update_mmu_cache_range(vma, addr, ptep, nr) > flush_dcache_folio(folio) > flush_icache_pages(vma, page, nr) > > flush_dcache_folio() isn't technically new, but no architecture > implemented it, so I've done that for them. The old APIs remain around > but are mostly implemented by calling the new interfaces. > > The new APIs are based around setting up N page table entries at once. > The N entries belong to the same PMD, the same folio and the same VMA, > so ptep++ is a legitimate operation, and locking is taken care of for > you. Some architectures can do a better job of it than just a loop, > but I have hesitated to make too deep a change to architectures I don't > understand well. > > One thing I have changed in every architecture is that PG_arch_1 is now a > per-folio bit instead of a per-page bit. This was something that would > have to happen eventually, and it makes sense to do it now rather than > iterate over every page involved in a cache flush and figure out if it > needs to happen. I think we do use PG_arch_1 on s390 for our secure page handling and making this perf folio instead of physical page really seems wrong and it probably breaks this code. Claudio, can you have a look?
On Tue, Jul 11, 2023 at 11:07:06AM +0200, Christian Borntraeger wrote: > Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle): > > This patchset changes the API used by the MM to set up page table entries. > > The four APIs are: > > set_ptes(mm, addr, ptep, pte, nr) > > update_mmu_cache_range(vma, addr, ptep, nr) > > flush_dcache_folio(folio) > > flush_icache_pages(vma, page, nr) > > > > flush_dcache_folio() isn't technically new, but no architecture > > implemented it, so I've done that for them. The old APIs remain around > > but are mostly implemented by calling the new interfaces. > > > > The new APIs are based around setting up N page table entries at once. > > The N entries belong to the same PMD, the same folio and the same VMA, > > so ptep++ is a legitimate operation, and locking is taken care of for > > you. Some architectures can do a better job of it than just a loop, > > but I have hesitated to make too deep a change to architectures I don't > > understand well. > > > > One thing I have changed in every architecture is that PG_arch_1 is now a > > per-folio bit instead of a per-page bit. This was something that would > > have to happen eventually, and it makes sense to do it now rather than > > iterate over every page involved in a cache flush and figure out if it > > needs to happen. > > I think we do use PG_arch_1 on s390 for our secure page handling and > making this perf folio instead of physical page really seems wrong > and it probably breaks this code. Per-page flags are going away in the next few years, so you're going to need a new design. s390 seems to do a lot of unusual things. I wish you'd talk to the rest of us more.
On Tue, 11 Jul 2023 13:36:27 +0100 Matthew Wilcox <willy@infradead.org> wrote: > On Tue, Jul 11, 2023 at 11:07:06AM +0200, Christian Borntraeger wrote: > > Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle): > > > This patchset changes the API used by the MM to set up page table entries. > > > The four APIs are: > > > set_ptes(mm, addr, ptep, pte, nr) > > > update_mmu_cache_range(vma, addr, ptep, nr) > > > flush_dcache_folio(folio) > > > flush_icache_pages(vma, page, nr) > > > > > > flush_dcache_folio() isn't technically new, but no architecture > > > implemented it, so I've done that for them. The old APIs remain around > > > but are mostly implemented by calling the new interfaces. > > > > > > The new APIs are based around setting up N page table entries at once. > > > The N entries belong to the same PMD, the same folio and the same VMA, > > > so ptep++ is a legitimate operation, and locking is taken care of for > > > you. Some architectures can do a better job of it than just a loop, > > > but I have hesitated to make too deep a change to architectures I don't > > > understand well. > > > > > > One thing I have changed in every architecture is that PG_arch_1 is now a > > > per-folio bit instead of a per-page bit. This was something that would > > > have to happen eventually, and it makes sense to do it now rather than > > > iterate over every page involved in a cache flush and figure out if it > > > needs to happen. > > > > I think we do use PG_arch_1 on s390 for our secure page handling and > > making this perf folio instead of physical page really seems wrong > > and it probably breaks this code. > > Per-page flags are going away in the next few years, so you're going to For each 4k physical page frame, we need to keep track whether it is secure or not. A bit in struct page seems the most logical choice. If that's not possible anymore, how would you propose we should do? > need a new design. s390 seems to do a lot of unusual things. I wish s390 is an unusual architecture. we are working on un-weirding our code, but it takes time > you'd talk to the rest of us more.
On Tue, 11 Jul 2023 17:24:40 +0200 Claudio Imbrenda <imbrenda@linux.ibm.com> wrote: > On Tue, 11 Jul 2023 13:36:27 +0100 > Matthew Wilcox <willy@infradead.org> wrote: > > > On Tue, Jul 11, 2023 at 11:07:06AM +0200, Christian Borntraeger wrote: > > > Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle): > > > > This patchset changes the API used by the MM to set up page table entries. > > > > The four APIs are: > > > > set_ptes(mm, addr, ptep, pte, nr) > > > > update_mmu_cache_range(vma, addr, ptep, nr) > > > > flush_dcache_folio(folio) > > > > flush_icache_pages(vma, page, nr) > > > > > > > > flush_dcache_folio() isn't technically new, but no architecture > > > > implemented it, so I've done that for them. The old APIs remain around > > > > but are mostly implemented by calling the new interfaces. > > > > > > > > The new APIs are based around setting up N page table entries at once. > > > > The N entries belong to the same PMD, the same folio and the same VMA, > > > > so ptep++ is a legitimate operation, and locking is taken care of for > > > > you. Some architectures can do a better job of it than just a loop, > > > > but I have hesitated to make too deep a change to architectures I don't > > > > understand well. > > > > > > > > One thing I have changed in every architecture is that PG_arch_1 is now a > > > > per-folio bit instead of a per-page bit. This was something that would > > > > have to happen eventually, and it makes sense to do it now rather than > > > > iterate over every page involved in a cache flush and figure out if it > > > > needs to happen. > > > > > > I think we do use PG_arch_1 on s390 for our secure page handling and > > > making this perf folio instead of physical page really seems wrong > > > and it probably breaks this code. > > > > Per-page flags are going away in the next few years, so you're going to > > For each 4k physical page frame, we need to keep track whether it is > secure or not. > > A bit in struct page seems the most logical choice. If that's not > possible anymore, how would you propose we should do? > > > need a new design. s390 seems to do a lot of unusual things. I wish > > s390 is an unusual architecture. we are working on un-weirding our > code, but it takes time > This issue sounds fatal for this version of this patchset?
On Tue, Jul 11, 2023 at 09:52:33AM -0700, Andrew Morton wrote: > On Tue, 11 Jul 2023 17:24:40 +0200 Claudio Imbrenda <imbrenda@linux.ibm.com> wrote: > > > On Tue, 11 Jul 2023 13:36:27 +0100 > > Matthew Wilcox <willy@infradead.org> wrote: > > > > > On Tue, Jul 11, 2023 at 11:07:06AM +0200, Christian Borntraeger wrote: > > > > Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle): > > > > > This patchset changes the API used by the MM to set up page table entries. > > > > > The four APIs are: > > > > > set_ptes(mm, addr, ptep, pte, nr) > > > > > update_mmu_cache_range(vma, addr, ptep, nr) > > > > > flush_dcache_folio(folio) > > > > > flush_icache_pages(vma, page, nr) > > > > > > > > > > flush_dcache_folio() isn't technically new, but no architecture > > > > > implemented it, so I've done that for them. The old APIs remain around > > > > > but are mostly implemented by calling the new interfaces. > > > > > > > > > > The new APIs are based around setting up N page table entries at once. > > > > > The N entries belong to the same PMD, the same folio and the same VMA, > > > > > so ptep++ is a legitimate operation, and locking is taken care of for > > > > > you. Some architectures can do a better job of it than just a loop, > > > > > but I have hesitated to make too deep a change to architectures I don't > > > > > understand well. > > > > > > > > > > One thing I have changed in every architecture is that PG_arch_1 is now a > > > > > per-folio bit instead of a per-page bit. This was something that would > > > > > have to happen eventually, and it makes sense to do it now rather than > > > > > iterate over every page involved in a cache flush and figure out if it > > > > > needs to happen. > > > > > > > > I think we do use PG_arch_1 on s390 for our secure page handling and > > > > making this perf folio instead of physical page really seems wrong > > > > and it probably breaks this code. > > > > > > Per-page flags are going away in the next few years, so you're going to > > > > For each 4k physical page frame, we need to keep track whether it is > > secure or not. > > > > A bit in struct page seems the most logical choice. If that's not > > possible anymore, how would you propose we should do? > > > > > need a new design. s390 seems to do a lot of unusual things. I wish > > > > s390 is an unusual architecture. we are working on un-weirding our > > code, but it takes time > > > > This issue sounds fatal for this version of this patchset? It's only declared as being per-folio in the cover letter to this patchset. I haven't done anything that will prohibit s390 from using it the way they do now. So it's not fatal, but it sounds like the in_range() macro might be ...
On Tue, Jul 11, 2023 at 05:24:40PM +0200, Claudio Imbrenda wrote: > On Tue, 11 Jul 2023 13:36:27 +0100 > Matthew Wilcox <willy@infradead.org> wrote: > > > I think we do use PG_arch_1 on s390 for our secure page handling and > > > making this perf folio instead of physical page really seems wrong > > > and it probably breaks this code. > > > > Per-page flags are going away in the next few years, so you're going to > > For each 4k physical page frame, we need to keep track whether it is > secure or not. Do you? Wouldn't it make more sense to track that per allocation instead of per page? ie if we allocate a 16kB anon folio for a VMA, don't you want the entire folio to be marked as secure vs insecure? I don't really know what secure means in this context. I think it has something to do with which of the VM or the hypervisor can access it, but it feels like something new that I've never had properly explained to me. > A bit in struct page seems the most logical choice. If that's not > possible anymore, how would you propose we should do? The plan is to shrink struct page down to a single pointer (which includes a few tag bits to say what type that pointer is -- a page table, anon mem, file mem, slab, etc). So there won't be any bits available for something like "secure or not". You could use a side structure if you really need to keep track on a per page basis.
On Wed, 12 Jul 2023 06:29:21 +0100 Matthew Wilcox <willy@infradead.org> wrote: > On Tue, Jul 11, 2023 at 05:24:40PM +0200, Claudio Imbrenda wrote: > > On Tue, 11 Jul 2023 13:36:27 +0100 > > Matthew Wilcox <willy@infradead.org> wrote: > > > > I think we do use PG_arch_1 on s390 for our secure page handling and > > > > making this perf folio instead of physical page really seems wrong > > > > and it probably breaks this code. > > > > > > Per-page flags are going away in the next few years, so you're going to > > > > For each 4k physical page frame, we need to keep track whether it is > > secure or not. > > Do you? Wouldn't it make more sense to track that per allocation instead no > of per page? ie if we allocate a 16kB anon folio for a VMA, don't you > want the entire folio to be marked as secure vs insecure? if we allocate a 16k folio, it would actually be initially marked as non-secure until the guest touches any of it, then only those 4k pages that are needed get marked as secure. the guest can also share the pages with the host, in which case the individual 4k pages get marked as non-secure once I/O is attempted on them (e.g. direct I/O) userspace (i.e. QEMU) can also try to look into the guest, causing individual pages to be exported (securely encrypted and then marked as non-secure) if they were secure and not shared. I/O cannot trigger exports, it will just fail, and that should not happen because in some cases it can bring down the whole system. Which is one of the main reasons why we need to keep track of the state. > > I don't really know what secure means in this context. I think it has > something to do with which of the VM or the hypervisor can access it, but > it feels like something new that I've never had properly explained to me. Secure means it belongs to a secure guest (confidential VM, protected virtualisation, Secure Execution, there are many names...). Hardware will prevent the host (or any other entity except for the secure guest itself) from accessing those 4k physical page frames, regardless of how the host might try. An exception will be presented for any attempts. I/O will not trigger any exception, and will instead just fail. I hope this explains why we need to track the property for each 4k physical page frame. > > > A bit in struct page seems the most logical choice. If that's not > > possible anymore, how would you propose we should do? > > The plan is to shrink struct page down to a single pointer (which interesting > includes a few tag bits to say what type that pointer is -- a page > table, anon mem, file mem, slab, etc). So there won't be any bits > available for something like "secure or not". You could use a side > structure if you really need to keep track on a per page basis. I guess that's something we will need to work on
Am 11.07.23 um 14:36 schrieb Matthew Wilcox: > On Tue, Jul 11, 2023 at 11:07:06AM +0200, Christian Borntraeger wrote: >> Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle): >>> This patchset changes the API used by the MM to set up page table entries. >>> The four APIs are: >>> set_ptes(mm, addr, ptep, pte, nr) >>> update_mmu_cache_range(vma, addr, ptep, nr) >>> flush_dcache_folio(folio) >>> flush_icache_pages(vma, page, nr) >>> >>> flush_dcache_folio() isn't technically new, but no architecture >>> implemented it, so I've done that for them. The old APIs remain around >>> but are mostly implemented by calling the new interfaces. >>> >>> The new APIs are based around setting up N page table entries at once. >>> The N entries belong to the same PMD, the same folio and the same VMA, >>> so ptep++ is a legitimate operation, and locking is taken care of for >>> you. Some architectures can do a better job of it than just a loop, >>> but I have hesitated to make too deep a change to architectures I don't >>> understand well. >>> >>> One thing I have changed in every architecture is that PG_arch_1 is now a >>> per-folio bit instead of a per-page bit. This was something that would >>> have to happen eventually, and it makes sense to do it now rather than >>> iterate over every page involved in a cache flush and figure out if it >>> needs to happen. >> >> I think we do use PG_arch_1 on s390 for our secure page handling and >> making this perf folio instead of physical page really seems wrong >> and it probably breaks this code. > > Per-page flags are going away in the next few years, so you're going to > need a new design. s390 seems to do a lot of unusual things. I wish > you'd talk to the rest of us more. I understand you point from a logical point of view, but a 4k page frame is also a hardware defined memory region. And I think not only for us. How do you want to implement hardware poisoning for example? Marking the whole folio with PG_hwpoison seems wrong.
On Thu, Jul 13, 2023 at 12:42:44PM +0200, Christian Borntraeger wrote: > > > Am 11.07.23 um 14:36 schrieb Matthew Wilcox: > > On Tue, Jul 11, 2023 at 11:07:06AM +0200, Christian Borntraeger wrote: > > > Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle): > > > > This patchset changes the API used by the MM to set up page table entries. > > > > The four APIs are: > > > > set_ptes(mm, addr, ptep, pte, nr) > > > > update_mmu_cache_range(vma, addr, ptep, nr) > > > > flush_dcache_folio(folio) > > > > flush_icache_pages(vma, page, nr) > > > > > > > > flush_dcache_folio() isn't technically new, but no architecture > > > > implemented it, so I've done that for them. The old APIs remain around > > > > but are mostly implemented by calling the new interfaces. > > > > > > > > The new APIs are based around setting up N page table entries at once. > > > > The N entries belong to the same PMD, the same folio and the same VMA, > > > > so ptep++ is a legitimate operation, and locking is taken care of for > > > > you. Some architectures can do a better job of it than just a loop, > > > > but I have hesitated to make too deep a change to architectures I don't > > > > understand well. > > > > > > > > One thing I have changed in every architecture is that PG_arch_1 is now a > > > > per-folio bit instead of a per-page bit. This was something that would > > > > have to happen eventually, and it makes sense to do it now rather than > > > > iterate over every page involved in a cache flush and figure out if it > > > > needs to happen. > > > > > > I think we do use PG_arch_1 on s390 for our secure page handling and > > > making this perf folio instead of physical page really seems wrong > > > and it probably breaks this code. > > > > Per-page flags are going away in the next few years, so you're going to > > need a new design. s390 seems to do a lot of unusual things. I wish > > you'd talk to the rest of us more. > > I understand you point from a logical point of view, but a 4k page frame > is also a hardware defined memory region. And I think not only for us. > How do you want to implement hardware poisoning for example? > Marking the whole folio with PG_hwpoison seems wrong. For hardware poison, we can't use the page for any other purpose any more. So one of the 16 types of pointer is for hardware poison. That doesn't seem like it's a solution that could work for secure/insecure pages? But what I'm really wondering is why you need to transition pages between secure/insecure on a 4kB boundary. What's the downside to doing it on a 16kB or 64kB boundary, or whatever size has been allocated?
Am 13.07.23 um 15:42 schrieb Matthew Wilcox: > On Thu, Jul 13, 2023 at 12:42:44PM +0200, Christian Borntraeger wrote: >> >> >> Am 11.07.23 um 14:36 schrieb Matthew Wilcox: >>> On Tue, Jul 11, 2023 at 11:07:06AM +0200, Christian Borntraeger wrote: >>>> Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle): >>>>> This patchset changes the API used by the MM to set up page table entries. >>>>> The four APIs are: >>>>> set_ptes(mm, addr, ptep, pte, nr) >>>>> update_mmu_cache_range(vma, addr, ptep, nr) >>>>> flush_dcache_folio(folio) >>>>> flush_icache_pages(vma, page, nr) >>>>> >>>>> flush_dcache_folio() isn't technically new, but no architecture >>>>> implemented it, so I've done that for them. The old APIs remain around >>>>> but are mostly implemented by calling the new interfaces. >>>>> >>>>> The new APIs are based around setting up N page table entries at once. >>>>> The N entries belong to the same PMD, the same folio and the same VMA, >>>>> so ptep++ is a legitimate operation, and locking is taken care of for >>>>> you. Some architectures can do a better job of it than just a loop, >>>>> but I have hesitated to make too deep a change to architectures I don't >>>>> understand well. >>>>> >>>>> One thing I have changed in every architecture is that PG_arch_1 is now a >>>>> per-folio bit instead of a per-page bit. This was something that would >>>>> have to happen eventually, and it makes sense to do it now rather than >>>>> iterate over every page involved in a cache flush and figure out if it >>>>> needs to happen. >>>> >>>> I think we do use PG_arch_1 on s390 for our secure page handling and >>>> making this perf folio instead of physical page really seems wrong >>>> and it probably breaks this code. >>> >>> Per-page flags are going away in the next few years, so you're going to >>> need a new design. s390 seems to do a lot of unusual things. I wish >>> you'd talk to the rest of us more. >> >> I understand you point from a logical point of view, but a 4k page frame >> is also a hardware defined memory region. And I think not only for us. >> How do you want to implement hardware poisoning for example? >> Marking the whole folio with PG_hwpoison seems wrong. > > For hardware poison, we can't use the page for any other purpose any more. > So one of the 16 types of pointer is for hardware poison. That doesn't > seem like it's a solution that could work for secure/insecure pages? > > But what I'm really wondering is why you need to transition pages > between secure/insecure on a 4kB boundary. What's the downside to doing > it on a 16kB or 64kB boundary, or whatever size has been allocated? The export and import for more pages will be more expensive, but I assume that we would then also use the larger chunks (e.g. for paging). The more interesting problem is that the guest can make a page shared/non-shared on a 4kb granularity. Stupid question: can folios be split into folio,single page,folio when needed?
On Thu, Jul 13, 2023 at 10:27:21PM +0200, Christian Borntraeger wrote: > > > Am 13.07.23 um 15:42 schrieb Matthew Wilcox: > > On Thu, Jul 13, 2023 at 12:42:44PM +0200, Christian Borntraeger wrote: > > > > > > > > > Am 11.07.23 um 14:36 schrieb Matthew Wilcox: > > > > On Tue, Jul 11, 2023 at 11:07:06AM +0200, Christian Borntraeger wrote: > > > > > Am 10.07.23 um 22:43 schrieb Matthew Wilcox (Oracle): > > > > > > This patchset changes the API used by the MM to set up page table entries. > > > > > > The four APIs are: > > > > > > set_ptes(mm, addr, ptep, pte, nr) > > > > > > update_mmu_cache_range(vma, addr, ptep, nr) > > > > > > flush_dcache_folio(folio) > > > > > > flush_icache_pages(vma, page, nr) > > > > > > > > > > > > flush_dcache_folio() isn't technically new, but no architecture > > > > > > implemented it, so I've done that for them. The old APIs remain around > > > > > > but are mostly implemented by calling the new interfaces. > > > > > > > > > > > > The new APIs are based around setting up N page table entries at once. > > > > > > The N entries belong to the same PMD, the same folio and the same VMA, > > > > > > so ptep++ is a legitimate operation, and locking is taken care of for > > > > > > you. Some architectures can do a better job of it than just a loop, > > > > > > but I have hesitated to make too deep a change to architectures I don't > > > > > > understand well. > > > > > > > > > > > > One thing I have changed in every architecture is that PG_arch_1 is now a > > > > > > per-folio bit instead of a per-page bit. This was something that would > > > > > > have to happen eventually, and it makes sense to do it now rather than > > > > > > iterate over every page involved in a cache flush and figure out if it > > > > > > needs to happen. > > > > > > > > > > I think we do use PG_arch_1 on s390 for our secure page handling and > > > > > making this perf folio instead of physical page really seems wrong > > > > > and it probably breaks this code. > > > > > > > > Per-page flags are going away in the next few years, so you're going to > > > > need a new design. s390 seems to do a lot of unusual things. I wish > > > > you'd talk to the rest of us more. > > > > > > I understand you point from a logical point of view, but a 4k page frame > > > is also a hardware defined memory region. And I think not only for us. > > > How do you want to implement hardware poisoning for example? > > > Marking the whole folio with PG_hwpoison seems wrong. > > > > For hardware poison, we can't use the page for any other purpose any more. > > So one of the 16 types of pointer is for hardware poison. That doesn't > > seem like it's a solution that could work for secure/insecure pages? > > > > But what I'm really wondering is why you need to transition pages > > between secure/insecure on a 4kB boundary. What's the downside to doing > > it on a 16kB or 64kB boundary, or whatever size has been allocated? > > The export and import for more pages will be more expensive, but I assume that > we would then also use the larger chunks (e.g. for paging). The more interesting > problem is that the guest can make a page shared/non-shared on a 4kb granularity. > > Stupid question: can folios be split into folio,single page,folio when needed? If that's a stupid question, you're going to find the answer utterly moronic ... Yes, we have split_folio() today. However, it can fail if somebody else has a reference to it, and if it does succeed, we don't really have a join_folio() operation (we have khugepaged which walks around looking for small folios it can replace with large folios, but that's not really what you want). In the MM of, let's say, 2025, I do intend to support what we might call a hole in a folio, precisely for hwpoison and it's beginning to sound a bit like it might work for you too. So you'd do something like ... Allocate a 256MB folio for your VM (probably one of many allocations you'd do to give your VM some memory). That sets 65536 page pointers to the same value. Then you "secure" all 256MB of it so the VM can use it all. Then the VM wants the host to read/write a 16kB chunk of that, so you allocate a "struct insecure_mem" and set four of the page pointers to point to that instead (it probably contains a copy of the original page pointer). We'd mark the folio as containing a hole so that the MM knows something unusual is going on. When you're done reading/writing the memory, you re-secure it, set the page pointers back to point to the original folio and free the struct insecure_mem. Would something like that work for you? Details TBD, of course.