Sean and Joao, thanks for the feedback. Probably we can drop this change. On Fri, Oct 9, 2020 at 6:28 PM Joao Martins <joao.m.martins@xxxxxxxxxx> wrote: > > On 10/9/20 1:58 AM, Sean Christopherson wrote: > > On Thu, Oct 08, 2020 at 03:54:12PM +0800, yulei.kernel@xxxxxxxxx wrote: > >> From: Yulei Zhang <yuleixzhang@xxxxxxxxxxx> > >> > >> Dmem page is pfn invalid but not mmio. Support cacheable > >> dmem page for kvm. > >> > >> Signed-off-by: Chen Zhuo <sagazchen@xxxxxxxxxxx> > >> Signed-off-by: Yulei Zhang <yuleixzhang@xxxxxxxxxxx> > >> --- > >> 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
