> -----Original Message----- > From: Tim Deegan [mailto:t...@xen.org] > Sent: 14 November 2018 12:42 > To: Jan Beulich <jbeul...@suse.com> > Cc: Paul Durrant <paul.durr...@citrix.com>; Andrew Cooper > <andrew.coop...@citrix.com>; Wei Liu <wei.l...@citrix.com>; xen-devel > <xen-devel@lists.xenproject.org> > Subject: Re: [PATCH 5/3] x86/shadow: emulate_gva_to_mfn() should respect > p2m_ioreq_server > > At 04:22 -0700 on 13 Nov (1542082936), Jan Beulich wrote: > > >>> On 13.11.18 at 11:59, <paul.durr...@citrix.com> wrote: > > >> Subject: [PATCH 5/3] x86/shadow: emulate_gva_to_mfn() should respect > > >> p2m_ioreq_server > > >> > > >> Writes to such pages would need to be handed to the emulator, which > we're > > >> not prepared to do at this point. > > >> > > >> Signed-off-by: Jan Beulich <jbeul...@suse.com> > > >> > > >> --- a/xen/arch/x86/mm/shadow/hvm.c > > >> +++ b/xen/arch/x86/mm/shadow/hvm.c > > >> @@ -338,7 +338,7 @@ static mfn_t emulate_gva_to_mfn(struct v > > >> { > > >> return _mfn(BAD_GFN_TO_MFN); > > >> } > > >> - if ( p2m_is_discard_write(p2mt) ) > > >> + if ( p2m_is_discard_write(p2mt) || p2mt == p2m_ioreq_server ) > > >> { > > >> put_page(page); > > >> return _mfn(READONLY_GFN); > > > > > > Is this what we want here? I would have thought we want to return > > > BAD_GFN_TO_MFN in the p2m_ioreq_server case so that the caller treats > this in > > > the same way it would MMIO. > > > > I'm not sure which behavior is better; I'm certainly fine with switching > > as you say, but I'd first like to see Tim's opinion as well. > > I'm not clear on what behaviour you want for this kind of page in > general -- I suspect I have missed or forgotten some context. If the > guest's not supposed to write to it, then IMO you should add it to > P2M_DISCARD_WRITE_TYPES rather than special-casing it here.
The type has an odd semantic... it needs to read as normal RAM but writes need to hit emulation. The use-case is for GVT-g where the emulator needs to intercept writes to the graphics pagetables in guest RAM. Paul _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
