Messages in this thread | | | Subject | Re: [Xen-devel] [PATCH] xen/p2m: fix extra memory regions accounting | From | Juergen Gross <> | Date | Thu, 3 Sep 2015 17:46:43 +0200 |
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On 09/03/2015 05:39 PM, Roger Pau Monné wrote: > El 03/09/15 a les 17.20, Juergen Gross ha escrit: >> On 09/03/2015 05:01 PM, David Vrabel wrote: >>> On 03/09/15 15:55, Juergen Gross wrote: >>>> On 09/03/2015 04:52 PM, David Vrabel wrote: >>>>> On 03/09/15 15:45, David Vrabel wrote: >>>>>> On 03/09/15 15:38, Roger Pau Monné wrote: >>>>>>> El 03/09/15 a les 14.25, Juergen Gross ha escrit: >>>>>>>> On 09/03/2015 02:05 PM, Roger Pau Monne wrote: >>>>>>>>> On systems with memory maps with ranges that don't end at page >>>>>>>>> boundaries, >>>>>>>>> like: >>>>>>>>> >>>>>>>>> [...] >>>>>>>>> (XEN) 0000000000100000 - 00000000dfdf9c00 (usable) >>>>>>>>> (XEN) 00000000dfdf9c00 - 00000000dfe4bc00 (ACPI NVS) >>>>>>>>> [...] >>>>>>>>> >>>>>>>>> xen_add_extra_mem will create a protected range that ends up at >>>>>>>>> 0xdfdf9c00, >>>>>>>>> but the function used to check if a memory address is inside of a >>>>>>>>> protected >>>>>>>>> range works with pfns, which means that an attempt to map >>>>>>>>> 0xdfdf9c00 >>>>>>>>> will be >>>>>>>>> refused because the check is performed against 0xdfdf9000 >>>>>>>>> instead of >>>>>>>>> 0xdfdf9c00. >>>>>>>>> >>>>>>>>> In order to fix this, make sure that the ranges that are added >>>>>>>>> to the >>>>>>>>> xen_extra_mem array are aligned to page boundaries. >>>>>>>>> >>>>>>>>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> >>>>>>>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> >>>>>>>>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> >>>>>>>>> Cc: David Vrabel <david.vrabel@citrix.com> >>>>>>>>> Cc: Juergen Gross <jgross@suse.com> >>>>>>>>> Cc: xen-devel@lists.xenproject.org >>>>>>>>> --- >>>>>>>>> AFAICT this patch needs to be backported to 3.19, 4.0, 4.1 and 4.2. >>>>>>>>> --- >>>>>>>>> arch/x86/xen/setup.c | 6 ++++++ >>>>>>>>> 1 file changed, 6 insertions(+) >>>>>>>>> >>>>>>>>> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c >>>>>>>>> index 55f388e..dcf5865 100644 >>>>>>>>> --- a/arch/x86/xen/setup.c >>>>>>>>> +++ b/arch/x86/xen/setup.c >>>>>>>>> @@ -68,6 +68,9 @@ static void __init xen_add_extra_mem(phys_addr_t >>>>>>>>> start, phys_addr_t size) >>>>>>>>> { >>>>>>>>> int i; >>>>>>>>> >>>>>>>>> + start = PAGE_ALIGN(start); >>>>>>>>> + size &= PAGE_MASK; >>>>>>>> >>>>>>>> This is not correct. If start wasn't page aligned and size was, >>>>>>>> you'll >>>>>>>> add one additional page to xen_extra_mem. >>>>>>> >>>>>>> I'm not understanding this, let's put an example: >>>>>>> >>>>>>> start = 0x8c00 >>>>>>> size = 0x1000 >>>>>>> >>>>>>> After the fixup added above this would become: >>>>>>> >>>>>>> start = 0x9000 >>>>>>> size = 0x1000 >>>>>>> >>>>>>> So if anything, I'm adding one page less (because 0x8000 was partly >>>>>>> added, and with the fixup it is not added). >>>>>> >>>>>> We expand the reserved (i.e., non-RAM) areas down so they're fully >>>>>> covered with whole pages when we depopulate and 1:1 map them, we >>>>>> should >>>>>> add extra memory regions that cover these same areas. >>>>> >>>>> Ignore this. This was nonsense. >>>>> >>>>> We expand the reserved (i.e., non-RAM) areas so they're fully covered >>>>> with whole pages when we depopulate and 1:1 map them, we should add the >>>>> extra memory such that it does not overlap with with expanded regions. >>>>> i.e., round up the start and round down the end (like Roger's patch >>>>> does). >>>> >>>> Nearly. Roger's patch rounds up start and rounds down the size. It might >>>> add non-RAM partial pages to xen_extra_mem. >>> >>> Yes. You're right. >> >> Hmm, thinking more about it, I'd prefer to change xen_extra_mem to use >> pfns instead of physical addresses. This would make things much more >> clear. >> >> Roger, do you want to do the patch or should I? > > I can certainly take care of it if you are busy, otherwise I leave it to > you since you have more expertise on it :).
Okay, I can do it. Should be ready soon...
Juergen
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