On 10/9/20 1:58 AM, Sean Christopherson wrote:
> On Thu, Oct 08, 2020 at 03:54:12PM +0800, yulei.ker...@gmail.com wrote:
>> From: Yulei Zhang <yuleixzh...@tencent.com>
>>
>> Dmem page is pfn invalid but not mmio. Support cacheable
>> dmem page for kvm.
>>
>> Signed-off-by: Chen Zhuo <sagazc...@tencent.com>
>> Signed-off-by: Yulei Zhang <yuleixzh...@tencent.com>
>> ---
>> arch/x86/kvm/mmu/mmu.c | 5 +++--
>> include/linux/dmem.h | 7 +++++++
>> mm/dmem.c | 7 +++++++
>> 3 files changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>> index 71aa3da2a0b7..0115c1767063 100644
>> --- a/arch/x86/kvm/mmu/mmu.c
>> +++ b/arch/x86/kvm/mmu/mmu.c
>> @@ -41,6 +41,7 @@
>> #include <linux/hash.h>
>> #include <linux/kern_levels.h>
>> #include <linux/kthread.h>
>> +#include <linux/dmem.h>
>>
>> #include <asm/page.h>
>> #include <asm/memtype.h>
>> @@ -2962,9 +2963,9 @@ static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
>> */
>> (!pat_enabled() || pat_pfn_immune_to_uc_mtrr(pfn));
>>
>> - return !e820__mapped_raw_any(pfn_to_hpa(pfn),
>> + return (!e820__mapped_raw_any(pfn_to_hpa(pfn),
>> pfn_to_hpa(pfn + 1) - 1,
>> - E820_TYPE_RAM);
>> + E820_TYPE_RAM)) || (!is_dmem_pfn(pfn));
>
> This is wrong. As is, the logic reads "A PFN is MMIO if it is INVALID &&
> (!RAM || !DMEM)". The obvious fix would be to change it to "INVALID &&
> !RAM && !DMEM", but that begs the question of whether or DMEM is reported
> as RAM. I don't see any e820 related changes in the series, i.e. no evidence
> that dmem yanks its memory out of the e820 tables, which makes me think this
> change is unnecessary.
>
Even if there would exist e820 changes, e820__mapped_raw_any() checks against
hardware-provided e820 that we are given before any changes happen i.e. not the
one kernel
has changed (e820_table_firmware). So unless you're having that memory carved
from an MMIO
range (which would be wrong), or the BIOS is misrepresenting its memory map...
the
e820__mapped_raw_any(E820_TYPE_RAM) ought to be enough to cover RAM.
Or at least that has been my experience with similar work.
Joao
